[gardening] Fix analyzer findings on observatory.

Follow-up to 6a6b9ac2bf25da95b42f41708297aa13a65c8f0b
TEST=ci

Change-Id: I8bda3591671ee1d0941d3313469c1df7095c03f1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427321
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
diff --git a/runtime/observatory/lib/app.dart b/runtime/observatory/lib/app.dart
index ecb46aa..4793714 100644
--- a/runtime/observatory/lib/app.dart
+++ b/runtime/observatory/lib/app.dart
@@ -20,7 +20,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
 import 'package:observatory/tracer.dart';
-import 'package:observatory/utils.dart';
 
 export 'package:observatory/utils.dart';
 
diff --git a/runtime/observatory/lib/src/elements/class_tree.dart b/runtime/observatory/lib/src/elements/class_tree.dart
index bb710ea..ff41ef7 100644
--- a/runtime/observatory/lib/src/elements/class_tree.dart
+++ b/runtime/observatory/lib/src/elements/class_tree.dart
@@ -8,7 +8,6 @@
 
 import 'package:web/web.dart';
 
-import 'package:observatory/app.dart';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/src/elements/class_ref.dart';
 import 'package:observatory/src/elements/containers/virtual_tree.dart';
diff --git a/runtime/observatory/lib/src/elements/class_view.dart b/runtime/observatory/lib/src/elements/class_view.dart
index c82128e..951569c 100644
--- a/runtime/observatory/lib/src/elements/class_view.dart
+++ b/runtime/observatory/lib/src/elements/class_view.dart
@@ -33,7 +33,6 @@
 import 'package:observatory/src/elements/object_common.dart';
 import 'package:observatory/src/elements/source_inset.dart';
 import 'package:observatory/src/elements/source_link.dart';
-import 'package:observatory/utils.dart';
 
 class ClassViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ClassViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/containers/search_bar.dart b/runtime/observatory/lib/src/elements/containers/search_bar.dart
index 513f87e..7bae1d1 100644
--- a/runtime/observatory/lib/src/elements/containers/search_bar.dart
+++ b/runtime/observatory/lib/src/elements/containers/search_bar.dart
@@ -7,7 +7,6 @@
 
 import 'package:web/web.dart';
 
-import 'package:observatory/app.dart';
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
diff --git a/runtime/observatory/lib/src/elements/containers/virtual_collection.dart b/runtime/observatory/lib/src/elements/containers/virtual_collection.dart
index 4f2efdf0..e586350 100644
--- a/runtime/observatory/lib/src/elements/containers/virtual_collection.dart
+++ b/runtime/observatory/lib/src/elements/containers/virtual_collection.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 typedef HTMLElement VirtualCollectionCreateCallback();
 typedef List<HTMLElement> VirtualCollectionHeaderCallback();
diff --git a/runtime/observatory/lib/src/elements/context_ref.dart b/runtime/observatory/lib/src/elements/context_ref.dart
index 3dcec9d..5f1f6b9 100644
--- a/runtime/observatory/lib/src/elements/context_ref.dart
+++ b/runtime/observatory/lib/src/elements/context_ref.dart
@@ -13,7 +13,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class ContextRefElement extends CustomElement implements Renderable {
   late RenderingScheduler<ContextRefElement> _r;
diff --git a/runtime/observatory/lib/src/elements/context_view.dart b/runtime/observatory/lib/src/elements/context_view.dart
index ba4cea4..bff8bd7 100644
--- a/runtime/observatory/lib/src/elements/context_view.dart
+++ b/runtime/observatory/lib/src/elements/context_view.dart
@@ -22,7 +22,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class ContextViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ContextViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart b/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
index d7ebadb..578bf5a 100644
--- a/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
+++ b/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
@@ -119,8 +119,6 @@
           throw new Exception('Unknown ProfileTreeMode: $mode');
         }
         break;
-      default:
-        throw new Exception('Unknown SampleProfileType: $type');
     }
     if (filters != null) {
       tree = filters!.fold(tree, (dynamic tree, filter) {
diff --git a/runtime/observatory/lib/src/elements/error_view.dart b/runtime/observatory/lib/src/elements/error_view.dart
index d0a3469..3fddd85 100644
--- a/runtime/observatory/lib/src/elements/error_view.dart
+++ b/runtime/observatory/lib/src/elements/error_view.dart
@@ -15,7 +15,6 @@
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
-import 'package:observatory/utils.dart';
 
 class ErrorViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ErrorViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/eval_box.dart b/runtime/observatory/lib/src/elements/eval_box.dart
index 971b576..f24da73 100644
--- a/runtime/observatory/lib/src/elements/eval_box.dart
+++ b/runtime/observatory/lib/src/elements/eval_box.dart
@@ -13,7 +13,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class EvalBoxElement extends CustomElement implements Renderable {
   late RenderingScheduler<EvalBoxElement> _r;
diff --git a/runtime/observatory/lib/src/elements/field_view.dart b/runtime/observatory/lib/src/elements/field_view.dart
index c431eec..bdf7e35 100644
--- a/runtime/observatory/lib/src/elements/field_view.dart
+++ b/runtime/observatory/lib/src/elements/field_view.dart
@@ -26,7 +26,6 @@
 import 'package:observatory/src/elements/object_common.dart';
 import 'package:observatory/src/elements/script_inset.dart';
 import 'package:observatory/src/elements/source_link.dart';
-import 'package:observatory/utils.dart';
 
 class FieldViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<FieldViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/flag_list.dart b/runtime/observatory/lib/src/elements/flag_list.dart
index 5fa11c8..bfde9a0 100644
--- a/runtime/observatory/lib/src/elements/flag_list.dart
+++ b/runtime/observatory/lib/src/elements/flag_list.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class FlagListElement extends CustomElement implements Renderable {
   late RenderingScheduler<FlagListElement> _r;
diff --git a/runtime/observatory/lib/src/elements/function_view.dart b/runtime/observatory/lib/src/elements/function_view.dart
index f988bae..3e4651f 100644
--- a/runtime/observatory/lib/src/elements/function_view.dart
+++ b/runtime/observatory/lib/src/elements/function_view.dart
@@ -28,7 +28,6 @@
 import 'package:observatory/src/elements/object_common.dart';
 import 'package:observatory/src/elements/source_inset.dart';
 import 'package:observatory/src/elements/source_link.dart';
-import 'package:observatory/utils.dart';
 
 class FunctionViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<FunctionViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/general_error.dart b/runtime/observatory/lib/src/elements/general_error.dart
index 857223c..826bdf6 100644
--- a/runtime/observatory/lib/src/elements/general_error.dart
+++ b/runtime/observatory/lib/src/elements/general_error.dart
@@ -15,7 +15,6 @@
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
-import 'package:observatory/utils.dart';
 
 class GeneralErrorElement extends CustomElement implements Renderable {
   late RenderingScheduler<GeneralErrorElement> _r;
diff --git a/runtime/observatory/lib/src/elements/heap_map.dart b/runtime/observatory/lib/src/elements/heap_map.dart
index 8920aed..27a029e 100644
--- a/runtime/observatory/lib/src/elements/heap_map.dart
+++ b/runtime/observatory/lib/src/elements/heap_map.dart
@@ -22,7 +22,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class HeapMapElement extends CustomElement implements Renderable {
   late RenderingScheduler<HeapMapElement> _r;
diff --git a/runtime/observatory/lib/src/elements/heap_snapshot.dart b/runtime/observatory/lib/src/elements/heap_snapshot.dart
index 06ed5fd..d80ad57 100644
--- a/runtime/observatory/lib/src/elements/heap_snapshot.dart
+++ b/runtime/observatory/lib/src/elements/heap_snapshot.dart
@@ -882,8 +882,6 @@
         _createTreeMap(
             report, new ClassesShallowDiffTreeMap(this, items), null);
         break;
-      default:
-        break;
     }
     return report;
   }
diff --git a/runtime/observatory/lib/src/elements/helpers/custom_element.dart b/runtime/observatory/lib/src/elements/helpers/custom_element.dart
index cf3cb99..a19bb21 100644
--- a/runtime/observatory/lib/src/elements/helpers/custom_element.dart
+++ b/runtime/observatory/lib/src/elements/helpers/custom_element.dart
@@ -7,7 +7,6 @@
 import 'package:web/web.dart';
 
 import 'package:observatory/src/elements/helpers/element_utils.dart';
-import 'package:observatory/utils.dart';
 
 HTMLElement element(CustomElement e) => e.element;
 
diff --git a/runtime/observatory/lib/src/elements/helpers/nav_bar.dart b/runtime/observatory/lib/src/elements/helpers/nav_bar.dart
index 58ce8c8..cc81f5b 100644
--- a/runtime/observatory/lib/src/elements/helpers/nav_bar.dart
+++ b/runtime/observatory/lib/src/elements/helpers/nav_bar.dart
@@ -5,7 +5,6 @@
 import 'package:web/web.dart';
 
 import 'package:observatory/src/elements/helpers/element_utils.dart';
-import 'package:observatory/utils.dart';
 
 HTMLElement navBar(List<HTMLElement> content) {
   return (document.createElement('nav')
diff --git a/runtime/observatory/lib/src/elements/icdata_ref.dart b/runtime/observatory/lib/src/elements/icdata_ref.dart
index 4bd90bf..a258aef 100644
--- a/runtime/observatory/lib/src/elements/icdata_ref.dart
+++ b/runtime/observatory/lib/src/elements/icdata_ref.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class ICDataRefElement extends CustomElement implements Renderable {
   late RenderingScheduler<ICDataRefElement> _r;
diff --git a/runtime/observatory/lib/src/elements/icdata_view.dart b/runtime/observatory/lib/src/elements/icdata_view.dart
index a42a32a..44cd817 100644
--- a/runtime/observatory/lib/src/elements/icdata_view.dart
+++ b/runtime/observatory/lib/src/elements/icdata_view.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class ICDataViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ICDataViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/inbound_references.dart b/runtime/observatory/lib/src/elements/inbound_references.dart
index 531829c..5134e68 100644
--- a/runtime/observatory/lib/src/elements/inbound_references.dart
+++ b/runtime/observatory/lib/src/elements/inbound_references.dart
@@ -12,7 +12,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class InboundReferencesElement extends CustomElement implements Renderable {
   late RenderingScheduler<InboundReferencesElement> _r;
diff --git a/runtime/observatory/lib/src/elements/isolate/counter_chart.dart b/runtime/observatory/lib/src/elements/isolate/counter_chart.dart
index e249414..40324b7 100644
--- a/runtime/observatory/lib/src/elements/isolate/counter_chart.dart
+++ b/runtime/observatory/lib/src/elements/isolate/counter_chart.dart
@@ -9,7 +9,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class IsolateCounterChartElement extends CustomElement implements Renderable {
   late RenderingScheduler<IsolateCounterChartElement> _r;
diff --git a/runtime/observatory/lib/src/elements/isolate_reconnect.dart b/runtime/observatory/lib/src/elements/isolate_reconnect.dart
index ebe1004..153cacf 100644
--- a/runtime/observatory/lib/src/elements/isolate_reconnect.dart
+++ b/runtime/observatory/lib/src/elements/isolate_reconnect.dart
@@ -16,7 +16,6 @@
 import 'package:observatory/src/elements/helpers/uris.dart';
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
-import 'package:observatory/utils.dart';
 
 class IsolateReconnectElement extends CustomElement implements Renderable {
   late RenderingScheduler<IsolateReconnectElement> _r;
diff --git a/runtime/observatory/lib/src/elements/isolate_view.dart b/runtime/observatory/lib/src/elements/isolate_view.dart
index 4b0c194..5e2f7a1 100644
--- a/runtime/observatory/lib/src/elements/isolate_view.dart
+++ b/runtime/observatory/lib/src/elements/isolate_view.dart
@@ -29,7 +29,6 @@
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/script_inset.dart';
 import 'package:observatory/src/elements/source_inset.dart';
-import 'package:observatory/utils.dart';
 
 class IsolateViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<IsolateViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/json_view.dart b/runtime/observatory/lib/src/elements/json_view.dart
index 55c6909..eb08253 100644
--- a/runtime/observatory/lib/src/elements/json_view.dart
+++ b/runtime/observatory/lib/src/elements/json_view.dart
@@ -15,7 +15,6 @@
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
-import 'package:observatory/utils.dart';
 
 class JSONViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<JSONViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/library_view.dart b/runtime/observatory/lib/src/elements/library_view.dart
index 7c9fc5f..bc98a16 100644
--- a/runtime/observatory/lib/src/elements/library_view.dart
+++ b/runtime/observatory/lib/src/elements/library_view.dart
@@ -29,7 +29,6 @@
 import 'package:observatory/src/elements/object_common.dart';
 import 'package:observatory/src/elements/script_inset.dart';
 import 'package:observatory/src/elements/script_ref.dart';
-import 'package:observatory/utils.dart';
 
 class LibraryViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<LibraryViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/logging.dart b/runtime/observatory/lib/src/elements/logging.dart
index 2bfd1e9..68d417c 100644
--- a/runtime/observatory/lib/src/elements/logging.dart
+++ b/runtime/observatory/lib/src/elements/logging.dart
@@ -21,7 +21,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class LoggingPageElement extends CustomElement implements Renderable {
   late RenderingScheduler<LoggingPageElement> _r;
diff --git a/runtime/observatory/lib/src/elements/megamorphiccache_ref.dart b/runtime/observatory/lib/src/elements/megamorphiccache_ref.dart
index f4a063b..f4017c3 100644
--- a/runtime/observatory/lib/src/elements/megamorphiccache_ref.dart
+++ b/runtime/observatory/lib/src/elements/megamorphiccache_ref.dart
@@ -10,7 +10,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 import 'package:observatory/models.dart' as M
     show IsolateRef, MegamorphicCacheRef;
diff --git a/runtime/observatory/lib/src/elements/megamorphiccache_view.dart b/runtime/observatory/lib/src/elements/megamorphiccache_view.dart
index 099c5be..37e4605 100644
--- a/runtime/observatory/lib/src/elements/megamorphiccache_view.dart
+++ b/runtime/observatory/lib/src/elements/megamorphiccache_view.dart
@@ -21,7 +21,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class MegamorphicCacheViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<MegamorphicCacheViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/metric/details.dart b/runtime/observatory/lib/src/elements/metric/details.dart
index 28209a5..4811237 100644
--- a/runtime/observatory/lib/src/elements/metric/details.dart
+++ b/runtime/observatory/lib/src/elements/metric/details.dart
@@ -10,7 +10,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class MetricDetailsElement extends CustomElement implements Renderable {
   late RenderingScheduler<MetricDetailsElement> _r;
diff --git a/runtime/observatory/lib/src/elements/metric/graph.dart b/runtime/observatory/lib/src/elements/metric/graph.dart
index b36e271..aefd220b 100644
--- a/runtime/observatory/lib/src/elements/metric/graph.dart
+++ b/runtime/observatory/lib/src/elements/metric/graph.dart
@@ -10,7 +10,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class MetricGraphElement extends CustomElement implements Renderable {
   late RenderingScheduler<MetricGraphElement> _r;
diff --git a/runtime/observatory/lib/src/elements/metrics.dart b/runtime/observatory/lib/src/elements/metrics.dart
index 636492d..353ae63 100644
--- a/runtime/observatory/lib/src/elements/metrics.dart
+++ b/runtime/observatory/lib/src/elements/metrics.dart
@@ -21,7 +21,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class MetricsPageElement extends CustomElement implements Renderable {
   late RenderingScheduler<MetricsPageElement> _r;
diff --git a/runtime/observatory/lib/src/elements/nav/menu_item.dart b/runtime/observatory/lib/src/elements/nav/menu_item.dart
index 15dfb4a..3220b10 100644
--- a/runtime/observatory/lib/src/elements/nav/menu_item.dart
+++ b/runtime/observatory/lib/src/elements/nav/menu_item.dart
@@ -9,7 +9,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class NavMenuItemElement extends CustomElement implements Renderable {
   late RenderingScheduler<NavMenuItemElement> _r;
diff --git a/runtime/observatory/lib/src/elements/nav/notify.dart b/runtime/observatory/lib/src/elements/nav/notify.dart
index 05b6051..24bbe1c 100644
--- a/runtime/observatory/lib/src/elements/nav/notify.dart
+++ b/runtime/observatory/lib/src/elements/nav/notify.dart
@@ -12,7 +12,6 @@
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/nav/notify_event.dart';
 import 'package:observatory/src/elements/nav/notify_exception.dart';
-import 'package:observatory/utils.dart';
 
 class NavNotifyElement extends CustomElement implements Renderable {
   late RenderingScheduler<NavNotifyElement> _r;
diff --git a/runtime/observatory/lib/src/elements/nav/notify_event.dart b/runtime/observatory/lib/src/elements/nav/notify_event.dart
index 21683be..b1d57710 100644
--- a/runtime/observatory/lib/src/elements/nav/notify_event.dart
+++ b/runtime/observatory/lib/src/elements/nav/notify_event.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class EventDeleteEvent {
   final M.Event event;
diff --git a/runtime/observatory/lib/src/elements/nav/notify_exception.dart b/runtime/observatory/lib/src/elements/nav/notify_exception.dart
index 8065924..250ab57 100644
--- a/runtime/observatory/lib/src/elements/nav/notify_exception.dart
+++ b/runtime/observatory/lib/src/elements/nav/notify_exception.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class ExceptionDeleteEvent {
   final dynamic exception;
diff --git a/runtime/observatory/lib/src/elements/nav/refresh.dart b/runtime/observatory/lib/src/elements/nav/refresh.dart
index 75acb99..4fa22f5 100644
--- a/runtime/observatory/lib/src/elements/nav/refresh.dart
+++ b/runtime/observatory/lib/src/elements/nav/refresh.dart
@@ -9,7 +9,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class RefreshEvent {
   final NavRefreshElement element;
diff --git a/runtime/observatory/lib/src/elements/object_view.dart b/runtime/observatory/lib/src/elements/object_view.dart
index a405470..07eb837 100644
--- a/runtime/observatory/lib/src/elements/object_view.dart
+++ b/runtime/observatory/lib/src/elements/object_view.dart
@@ -18,7 +18,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class ObjectViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ObjectViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/objectpool_ref.dart b/runtime/observatory/lib/src/elements/objectpool_ref.dart
index 775fa5e..4a48d6f 100644
--- a/runtime/observatory/lib/src/elements/objectpool_ref.dart
+++ b/runtime/observatory/lib/src/elements/objectpool_ref.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class ObjectPoolRefElement extends CustomElement implements Renderable {
   late RenderingScheduler<ObjectPoolRefElement> _r;
diff --git a/runtime/observatory/lib/src/elements/objectpool_view.dart b/runtime/observatory/lib/src/elements/objectpool_view.dart
index 653b5af..703df04 100644
--- a/runtime/observatory/lib/src/elements/objectpool_view.dart
+++ b/runtime/observatory/lib/src/elements/objectpool_view.dart
@@ -21,7 +21,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class ObjectPoolViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ObjectPoolViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/objectstore_view.dart b/runtime/observatory/lib/src/elements/objectstore_view.dart
index 772b26a..3543819 100644
--- a/runtime/observatory/lib/src/elements/objectstore_view.dart
+++ b/runtime/observatory/lib/src/elements/objectstore_view.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class ObjectStoreViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ObjectStoreViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/ports.dart b/runtime/observatory/lib/src/elements/ports.dart
index e73f604..e28c90e 100644
--- a/runtime/observatory/lib/src/elements/ports.dart
+++ b/runtime/observatory/lib/src/elements/ports.dart
@@ -18,7 +18,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class PortsElement extends CustomElement implements Renderable {
   late RenderingScheduler<PortsElement> _r;
diff --git a/runtime/observatory/lib/src/elements/process_snapshot.dart b/runtime/observatory/lib/src/elements/process_snapshot.dart
index 05b0d64..f28d071 100644
--- a/runtime/observatory/lib/src/elements/process_snapshot.dart
+++ b/runtime/observatory/lib/src/elements/process_snapshot.dart
@@ -429,8 +429,6 @@
         _tree!.expand(root);
         report.add(_tree!.element);
         break;
-      default:
-        throw new Exception('Unknown ProcessSnapshotTreeMode: $_mode');
     }
 
     return report;
diff --git a/runtime/observatory/lib/src/elements/retaining_path.dart b/runtime/observatory/lib/src/elements/retaining_path.dart
index 0a2a868..32931af 100644
--- a/runtime/observatory/lib/src/elements/retaining_path.dart
+++ b/runtime/observatory/lib/src/elements/retaining_path.dart
@@ -12,7 +12,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class RetainingPathElement extends CustomElement implements Renderable {
   late RenderingScheduler<RetainingPathElement> _r;
diff --git a/runtime/observatory/lib/src/elements/script_view.dart b/runtime/observatory/lib/src/elements/script_view.dart
index 75f5edb..ecdd0e0 100644
--- a/runtime/observatory/lib/src/elements/script_view.dart
+++ b/runtime/observatory/lib/src/elements/script_view.dart
@@ -22,7 +22,6 @@
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
 import 'package:observatory/src/elements/script_inset.dart';
-import 'package:observatory/utils.dart';
 
 class ScriptViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<ScriptViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/sentinel_view.dart b/runtime/observatory/lib/src/elements/sentinel_view.dart
index eedfc97..0abcb91 100644
--- a/runtime/observatory/lib/src/elements/sentinel_view.dart
+++ b/runtime/observatory/lib/src/elements/sentinel_view.dart
@@ -16,7 +16,6 @@
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class SentinelViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<SentinelViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/singletargetcache_ref.dart b/runtime/observatory/lib/src/elements/singletargetcache_ref.dart
index e4f9a08..cb29be5 100644
--- a/runtime/observatory/lib/src/elements/singletargetcache_ref.dart
+++ b/runtime/observatory/lib/src/elements/singletargetcache_ref.dart
@@ -10,7 +10,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 import 'package:observatory/models.dart' as M
     show IsolateRef, SingleTargetCacheRef;
diff --git a/runtime/observatory/lib/src/elements/singletargetcache_view.dart b/runtime/observatory/lib/src/elements/singletargetcache_view.dart
index d78dcca..b7a62de 100644
--- a/runtime/observatory/lib/src/elements/singletargetcache_view.dart
+++ b/runtime/observatory/lib/src/elements/singletargetcache_view.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class SingleTargetCacheViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<SingleTargetCacheViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/stack_trace_tree_config.dart b/runtime/observatory/lib/src/elements/stack_trace_tree_config.dart
index d240b11..617e447 100644
--- a/runtime/observatory/lib/src/elements/stack_trace_tree_config.dart
+++ b/runtime/observatory/lib/src/elements/stack_trace_tree_config.dart
@@ -10,7 +10,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 enum ProfileTreeMode {
   code,
diff --git a/runtime/observatory/lib/src/elements/strongly_reachable_instances.dart b/runtime/observatory/lib/src/elements/strongly_reachable_instances.dart
index 3bbc57f..8bb1256 100644
--- a/runtime/observatory/lib/src/elements/strongly_reachable_instances.dart
+++ b/runtime/observatory/lib/src/elements/strongly_reachable_instances.dart
@@ -12,7 +12,6 @@
 import 'package:observatory/src/elements/helpers/custom_element.dart';
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
-import 'package:observatory/utils.dart';
 
 class StronglyReachableInstancesElement extends CustomElement
     implements Renderable {
diff --git a/runtime/observatory/lib/src/elements/subtypetestcache_view.dart b/runtime/observatory/lib/src/elements/subtypetestcache_view.dart
index f1eeedc..ba5b3be 100644
--- a/runtime/observatory/lib/src/elements/subtypetestcache_view.dart
+++ b/runtime/observatory/lib/src/elements/subtypetestcache_view.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class SubtypeTestCacheViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<SubtypeTestCacheViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/timeline_page.dart b/runtime/observatory/lib/src/elements/timeline_page.dart
index 3422201..0c76066 100644
--- a/runtime/observatory/lib/src/elements/timeline_page.dart
+++ b/runtime/observatory/lib/src/elements/timeline_page.dart
@@ -21,7 +21,6 @@
 import 'package:observatory/src/elements/nav/refresh.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
-import 'package:observatory/utils.dart';
 
 class TimelinePageElement extends CustomElement implements Renderable {
   late RenderingScheduler<TimelinePageElement> _r;
diff --git a/runtime/observatory/lib/src/elements/unlinkedcall_ref.dart b/runtime/observatory/lib/src/elements/unlinkedcall_ref.dart
index 1581e2e..b417542 100644
--- a/runtime/observatory/lib/src/elements/unlinkedcall_ref.dart
+++ b/runtime/observatory/lib/src/elements/unlinkedcall_ref.dart
@@ -11,7 +11,6 @@
 import 'package:observatory/src/elements/helpers/element_utils.dart';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
-import 'package:observatory/utils.dart';
 
 class UnlinkedCallRefElement extends CustomElement implements Renderable {
   late RenderingScheduler<UnlinkedCallRefElement> _r;
diff --git a/runtime/observatory/lib/src/elements/unlinkedcall_view.dart b/runtime/observatory/lib/src/elements/unlinkedcall_view.dart
index 0d5501c..26ae67c 100644
--- a/runtime/observatory/lib/src/elements/unlinkedcall_view.dart
+++ b/runtime/observatory/lib/src/elements/unlinkedcall_view.dart
@@ -19,7 +19,6 @@
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/nav/vm_menu.dart';
 import 'package:observatory/src/elements/object_common.dart';
-import 'package:observatory/utils.dart';
 
 class UnlinkedCallViewElement extends CustomElement implements Renderable {
   late RenderingScheduler<UnlinkedCallViewElement> _r;
diff --git a/runtime/observatory/lib/src/elements/vm_connect.dart b/runtime/observatory/lib/src/elements/vm_connect.dart
index d178c06..e8594e5 100644
--- a/runtime/observatory/lib/src/elements/vm_connect.dart
+++ b/runtime/observatory/lib/src/elements/vm_connect.dart
@@ -16,7 +16,6 @@
 import 'package:observatory/src/elements/nav/notify.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 import 'package:observatory/src/elements/vm_connect_target.dart';
-import 'package:observatory/utils.dart';
 
 class VMConnectElement extends CustomElement implements Renderable {
   late RenderingScheduler<VMConnectElement> _r;
diff --git a/runtime/observatory/pubspec.yaml b/runtime/observatory/pubspec.yaml
index 08505da..31eadc2 100644
--- a/runtime/observatory/pubspec.yaml
+++ b/runtime/observatory/pubspec.yaml
@@ -1,7 +1,7 @@
 name: observatory
 
 environment:
-  sdk: ^2.19.0
+  sdk: ^3.5.0
 
 # dependencies:
 
diff --git a/runtime/observatory/tests/service/auth_token_test.dart b/runtime/observatory/tests/service/auth_token_test.dart
index 0218fcb..0ee49c3 100644
--- a/runtime/observatory/tests/service/auth_token_test.dart
+++ b/runtime/observatory/tests/service/auth_token_test.dart
@@ -29,7 +29,7 @@
   var url = Uri.parse('http://localhost:$port');
   var httpClient = new io.HttpClient();
   try {
-    var request = await httpClient.getUrl(url);
+    await httpClient.getUrl(url);
     fail('expected exception');
   } catch (e) {
     // Expected
@@ -37,7 +37,7 @@
 
   // Try connecting to the server with the auth token, it should succeed.
   try {
-    var request = await httpClient.getUrl(info.serverUri!);
+    await httpClient.getUrl(info.serverUri!);
   } catch (e) {
     fail('could not connect');
   }
diff --git a/runtime/observatory/tests/service/breakpoint_on_simple_conditions_test.dart b/runtime/observatory/tests/service/breakpoint_on_simple_conditions_test.dart
index 526f0d5..c598a7e 100644
--- a/runtime/observatory/tests/service/breakpoint_on_simple_conditions_test.dart
+++ b/runtime/observatory/tests/service/breakpoint_on_simple_conditions_test.dart
@@ -12,14 +12,14 @@
 
 testMain() {
   bool foo = false;
-  if (foo) {} // LINE_A
+  if (foo) {} // ignore:dead_code LINE_A
 
   const bar = false;
-  if (bar) {} // LINE_B
+  if (bar) {} // ignore:dead_code LINE_B
 
-  while (foo) {} // LINE_C
+  while (foo) {} // ignore:dead_code LINE_C
 
-  while (bar) {} // LINE_D
+  while (bar) {} // ignore:dead_code LINE_D
 }
 
 var tests = [
diff --git a/runtime/observatory/tests/service/breakpoints_with_mixin_lib1.dart b/runtime/observatory/tests/service/breakpoints_with_mixin_lib1.dart
index 3c43715..af84289 100644
--- a/runtime/observatory/tests/service/breakpoints_with_mixin_lib1.dart
+++ b/runtime/observatory/tests/service/breakpoints_with_mixin_lib1.dart
@@ -4,4 +4,4 @@
 
 import "breakpoints_with_mixin_lib3.dart";
 
-class Test1 extends Object with Foo {}
+class Test1 extends Object with FooMixin {}
diff --git a/runtime/observatory/tests/service/breakpoints_with_mixin_lib2.dart b/runtime/observatory/tests/service/breakpoints_with_mixin_lib2.dart
index c054176..628188d 100644
--- a/runtime/observatory/tests/service/breakpoints_with_mixin_lib2.dart
+++ b/runtime/observatory/tests/service/breakpoints_with_mixin_lib2.dart
@@ -4,4 +4,4 @@
 
 import "breakpoints_with_mixin_lib3.dart";
 
-class Test2 extends Object with Foo {}
+class Test2 extends Object with FooMixin {}
diff --git a/runtime/observatory/tests/service/breakpoints_with_mixin_lib3.dart b/runtime/observatory/tests/service/breakpoints_with_mixin_lib3.dart
index a7329de..750301c 100644
--- a/runtime/observatory/tests/service/breakpoints_with_mixin_lib3.dart
+++ b/runtime/observatory/tests/service/breakpoints_with_mixin_lib3.dart
@@ -13,3 +13,9 @@
     print("I should be breakable too!");
   }
 }
+
+mixin FooMixin {
+  foo() {
+    print("I should be breakable!");
+  }
+}
diff --git a/runtime/observatory/tests/service/breakpoints_with_mixin_test.dart b/runtime/observatory/tests/service/breakpoints_with_mixin_test.dart
index 887c5f9..ea2b57e 100644
--- a/runtime/observatory/tests/service/breakpoints_with_mixin_test.dart
+++ b/runtime/observatory/tests/service/breakpoints_with_mixin_test.dart
@@ -14,16 +14,17 @@
 //
 // dart pkg/vm_service/test/update_line_numbers.dart runtime/observatory/tests/service/breakpoints_with_mixin_test.dart
 //
-const LINE_A = 25;
+const LINE_A = 26;
 // AUTOGENERATED END
 
 const String testFilename = "breakpoints_with_mixin_test.dart";
 const String lib3Filename = "breakpoints_with_mixin_lib3.dart";
 const int lib3Bp1 = 7;
 const int lib3Bp2 = 13;
+const int lib3Bp3 = 19;
 
 void code() { // LINE_A
-  Test1 test1 = new Test1();  
+  Test1 test1 = new Test1();
   test1.foo();
   Test2 test2 = new Test2();
   test2.foo();
@@ -40,12 +41,12 @@
 List<String> stops = [];
 
 List<String> expected = [
-  "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 2}:9)",
-  "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 4}:9)",
+  "$lib3Filename:$lib3Bp3:5 ($testFilename:${LINE_A + 2}:9)",
+  "$lib3Filename:$lib3Bp3:5 ($testFilename:${LINE_A + 4}:9)",
   "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 6}:7)",
   "$lib3Filename:$lib3Bp2:5 ($testFilename:${LINE_A + 8}:7)",
-  "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 9}:9)",
-  "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 10}:9)",
+  "$lib3Filename:$lib3Bp3:5 ($testFilename:${LINE_A + 9}:9)",
+  "$lib3Filename:$lib3Bp3:5 ($testFilename:${LINE_A + 10}:9)",
   "$lib3Filename:$lib3Bp1:5 ($testFilename:${LINE_A + 11}:7)",
   "$lib3Filename:$lib3Bp2:5 ($testFilename:${LINE_A + 12}:7)",
 ];
@@ -54,6 +55,7 @@
   hasPausedAtStart,
   setBreakpointAtUriAndLine(lib3Filename, lib3Bp1),
   setBreakpointAtUriAndLine(lib3Filename, lib3Bp2),
+  setBreakpointAtUriAndLine(lib3Filename, lib3Bp3),
   resumeProgramRecordingStops(stops, true),
   checkRecordedStops(stops, expected)
 ];
diff --git a/runtime/observatory/tests/service/developer_service_get_isolate_id_test.dart b/runtime/observatory/tests/service/developer_service_get_isolate_id_test.dart
index 093ea97..54b2cec 100644
--- a/runtime/observatory/tests/service/developer_service_get_isolate_id_test.dart
+++ b/runtime/observatory/tests/service/developer_service_get_isolate_id_test.dart
@@ -27,8 +27,8 @@
   childIsolate = await Core.Isolate.spawn(spawnEntry, 0);
   // Assign the id for this isolate and it's child to strings so they can
   // be read by the tester.
-  selfId = dev.Service.getIsolateID(Core.Isolate.current)!;
-  childId = dev.Service.getIsolateID(childIsolate)!;
+  selfId = dev.Service.getIsolateId(Core.Isolate.current)!;
+  childId = dev.Service.getIsolateId(childIsolate)!;
   dev.debugger();
 }
 
diff --git a/runtime/observatory/tests/service/evaluate_expression_with_optimized_out_receiver_on_stack_test.dart b/runtime/observatory/tests/service/evaluate_expression_with_optimized_out_receiver_on_stack_test.dart
index ee0e71c..b7c9310 100644
--- a/runtime/observatory/tests/service/evaluate_expression_with_optimized_out_receiver_on_stack_test.dart
+++ b/runtime/observatory/tests/service/evaluate_expression_with_optimized_out_receiver_on_stack_test.dart
@@ -13,8 +13,6 @@
 
 import 'dart:_internal'; // ignore: import_internal_library, unused_import
 
-
-
 String examineStackExpression(String variableName) {
   // The returned string is the evaluation expression. We try to make it so that
   // the evaluated expression exercises OSR, Deopt, StackTrace.
diff --git a/runtime/observatory/tests/service/evaluate_in_mixin_application_alias_frame_test.dart b/runtime/observatory/tests/service/evaluate_in_mixin_application_alias_frame_test.dart
index ba21df2..9010084 100644
--- a/runtime/observatory/tests/service/evaluate_in_mixin_application_alias_frame_test.dart
+++ b/runtime/observatory/tests/service/evaluate_in_mixin_application_alias_frame_test.dart
@@ -15,7 +15,7 @@
 
 class S {}
 
-class M {
+mixin M {
   static String? foo;
   bar() {
     foo = "theExpectedValue";
diff --git a/runtime/observatory/tests/service/evaluate_in_mixin_application_frame_test.dart b/runtime/observatory/tests/service/evaluate_in_mixin_application_frame_test.dart
index 5409402..deba927 100644
--- a/runtime/observatory/tests/service/evaluate_in_mixin_application_frame_test.dart
+++ b/runtime/observatory/tests/service/evaluate_in_mixin_application_frame_test.dart
@@ -15,7 +15,7 @@
 
 class S {}
 
-class M {
+mixin M {
   static String? foo;
   bar() {
     foo = "theExpectedValue";
diff --git a/runtime/observatory/tests/service/evaluate_on_mixin_application_alias_test.dart b/runtime/observatory/tests/service/evaluate_on_mixin_application_alias_test.dart
index 141213d..ede7bc7 100644
--- a/runtime/observatory/tests/service/evaluate_on_mixin_application_alias_test.dart
+++ b/runtime/observatory/tests/service/evaluate_on_mixin_application_alias_test.dart
@@ -12,7 +12,7 @@
 
 class S {}
 
-class M {
+mixin M {
   static String? foo;
   bar() {
     foo = "theExpectedValue";
diff --git a/runtime/observatory/tests/service/evaluate_on_mixin_application_test.dart b/runtime/observatory/tests/service/evaluate_on_mixin_application_test.dart
index e114df2..0b3aed4 100644
--- a/runtime/observatory/tests/service/evaluate_on_mixin_application_test.dart
+++ b/runtime/observatory/tests/service/evaluate_on_mixin_application_test.dart
@@ -12,7 +12,7 @@
 
 class S {}
 
-class M {
+mixin M {
   static String? foo;
   bar() {
     foo = "theExpectedValue";
diff --git a/runtime/observatory/tests/service/evaluate_type_arguments_test.dart b/runtime/observatory/tests/service/evaluate_type_arguments_test.dart
index 93a98f5..280a0a6 100644
--- a/runtime/observatory/tests/service/evaluate_type_arguments_test.dart
+++ b/runtime/observatory/tests/service/evaluate_type_arguments_test.dart
@@ -45,7 +45,7 @@
 }
 
 void fooxx<E extends String>(List<E> y) {
-  List<E> x = new List<E>.from(["hello"]);
+  List<E> x = new List<E>.from(["hello"]);  // ignore:unused_local_variable
 }
 
 var tests = <IsolateTest>[
diff --git a/runtime/observatory/tests/service/fetch_all_types_test.dart b/runtime/observatory/tests/service/fetch_all_types_test.dart
index f3d4ef6..4df5ea9 100644
--- a/runtime/observatory/tests/service/fetch_all_types_test.dart
+++ b/runtime/observatory/tests/service/fetch_all_types_test.dart
@@ -18,7 +18,7 @@
 
       Class cls = entry["class"];
       print(cls);
-      dynamic rawInstanceSet = await isolate.invokeRpcNoUpgrade(
+      await isolate.invokeRpcNoUpgrade(
           'getInstances', {'objectId': cls.id, 'limit': 10});
       dynamic instanceSet = await isolate.getInstances(cls, 10);
       for (var instance in instanceSet.instances) {
diff --git a/runtime/observatory/tests/service/get_object_rpc_test.dart b/runtime/observatory/tests/service/get_object_rpc_test.dart
index 1997e4b..5d784e7 100644
--- a/runtime/observatory/tests/service/get_object_rpc_test.dart
+++ b/runtime/observatory/tests/service/get_object_rpc_test.dart
@@ -17,9 +17,9 @@
 }
 
 class _DummyClass extends _DummyAbstractBaseClass {
-  static var dummyVar = 11;
+  static var dummyVar = 11; // ignore: unused_field
   final List<String> dummyList = new List<String>.filled(20, '');
-  static var dummyVarWithInit = foo();
+  static var dummyVarWithInit = foo(); // ignore: unused_field
   late String dummyLateVarWithInit = 'bar';
   late String dummyLateVar;
   @override
diff --git a/runtime/observatory/tests/service/issue_30555_test.dart b/runtime/observatory/tests/service/issue_30555_test.dart
index 72adf54..55744f8 100644
--- a/runtime/observatory/tests/service/issue_30555_test.dart
+++ b/runtime/observatory/tests/service/issue_30555_test.dart
@@ -123,7 +123,6 @@
         default:
           fail("Shouldn't get here, the second isolate resumed even though it "
               "was not expect to do it");
-          break;
       }
       step++;
     });
diff --git a/runtime/observatory/tests/service/library_dependency_test.dart b/runtime/observatory/tests/service/library_dependency_test.dart
index ff829a9..1549f83 100644
--- a/runtime/observatory/tests/service/library_dependency_test.dart
+++ b/runtime/observatory/tests/service/library_dependency_test.dart
@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:mirrors' as mirrors;
-import 'dart:convert' deferred as convert;
+import 'dart:convert' deferred as convert;  // ignore: unused_import
 
 import 'package:test/test.dart';
 
diff --git a/runtime/observatory/tests/service/local_variable_declaration_test.dart b/runtime/observatory/tests/service/local_variable_declaration_test.dart
index d8bacb6..69035a7 100644
--- a/runtime/observatory/tests/service/local_variable_declaration_test.dart
+++ b/runtime/observatory/tests/service/local_variable_declaration_test.dart
@@ -16,9 +16,9 @@
 }
 
 testMain() {
-  int? xxx, yyyy, zzzzz;
+  int? xxx, yyyy, zzzzz; // ignore: unused_local_variable
   for (int i = 0; i < 1; i++) {
-    var foo = () {};
+    var foo = () {}; // ignore: unused_local_variable
     debugger();
   }
   var bar = () {
diff --git a/runtime/observatory/tests/service/mixin_break_mixin_class.dart b/runtime/observatory/tests/service/mixin_break_mixin_class.dart
index e19a7a8..142491d 100644
--- a/runtime/observatory/tests/service/mixin_break_mixin_class.dart
+++ b/runtime/observatory/tests/service/mixin_break_mixin_class.dart
@@ -1,6 +1,6 @@
 library mixin_step_mixin_class;
 
-class HelloMixin {
+mixin HelloMixin {
   void sayHello() {
     print("Hello!");
   }
diff --git a/runtime/observatory/tests/service/next_through_await_for_test.dart b/runtime/observatory/tests/service/next_through_await_for_test.dart
index 8118375..16917d1 100644
--- a/runtime/observatory/tests/service/next_through_await_for_test.dart
+++ b/runtime/observatory/tests/service/next_through_await_for_test.dart
@@ -11,7 +11,7 @@
 const String file = "next_through_await_for_test.dart";
 
 code() async {
-  int count = 0;
+  int count = 0; // ignore: unused_local_variable
   await for (var num in naturalsTo(2)) {
     print(num);
     count++;
diff --git a/runtime/observatory/tests/service/pause_on_unhandled_async_exceptions_zones_test.dart b/runtime/observatory/tests/service/pause_on_unhandled_async_exceptions_zones_test.dart
index e15ec92..12cc89e 100644
--- a/runtime/observatory/tests/service/pause_on_unhandled_async_exceptions_zones_test.dart
+++ b/runtime/observatory/tests/service/pause_on_unhandled_async_exceptions_zones_test.dart
@@ -23,7 +23,7 @@
 
 String doThrow() {
   throw "TheException";
-  return "end of doThrow";
+  return "end of doThrow"; // ignore: dead_code
 }
 
 Future<void> asyncThrower() async {
diff --git a/runtime/observatory/tests/service/regress_34841_lib.dart b/runtime/observatory/tests/service/regress_34841_lib.dart
index 60eb3e4..e0a1fb8 100644
--- a/runtime/observatory/tests/service/regress_34841_lib.dart
+++ b/runtime/observatory/tests/service/regress_34841_lib.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-class Foo {
+mixin Foo {
   String baz() => StackTrace.current.toString();
   final String foo = () {
     return StackTrace.current.toString();