Observatory strong mode fix: Use .nodes= instead of .children= to accommodate text nodes.

This is necessary because HtmlElement.children= requires its parameter
type to be a List<Element>, and text nodes are not elements.

Change-Id: I99c91fe060c16f02d737d904f6869b3dad19c196
Reviewed-on: https://dart-review.googlesource.com/57005
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
diff --git a/runtime/observatory/lib/src/elements/containers/search_bar.dart b/runtime/observatory/lib/src/elements/containers/search_bar.dart
index 3db5c16..e3cc4ea 100644
--- a/runtime/observatory/lib/src/elements/containers/search_bar.dart
+++ b/runtime/observatory/lib/src/elements/containers/search_bar.dart
@@ -138,7 +138,7 @@
           })
       ];
     }
-    _resultsArea.children = [
+    _resultsArea.nodes = [
       new ButtonElement()
         ..text = '▲'
         ..disabled = _results.isEmpty
diff --git a/runtime/observatory/lib/src/elements/memory/allocations.dart b/runtime/observatory/lib/src/elements/memory/allocations.dart
index 64f9595..ad3c5dd 100644
--- a/runtime/observatory/lib/src/elements/memory/allocations.dart
+++ b/runtime/observatory/lib/src/elements/memory/allocations.dart
@@ -161,7 +161,7 @@
         ..children = [
           new SpanElement()
             ..classes = ['group']
-            ..children = [
+            ..nodes = [
               new Text('Since Last '),
               resetAccumulators
                 ..text = 'Reset'
diff --git a/runtime/observatory/lib/src/elements/memory/profile.dart b/runtime/observatory/lib/src/elements/memory/profile.dart
index 9a87ab2..4a4f1d8 100644
--- a/runtime/observatory/lib/src/elements/memory/profile.dart
+++ b/runtime/observatory/lib/src/elements/memory/profile.dart
@@ -108,7 +108,7 @@
         ..classes = ['content-centered-big']
         ..children = [
           new HeadingElement.h1()
-            ..children = [
+            ..nodes = [
               new Text(_isolate.name),
               bReload
                 ..classes = ['header_button']
diff --git a/runtime/observatory/lib/src/elements/timeline/dashboard.dart b/runtime/observatory/lib/src/elements/timeline/dashboard.dart
index bfa7f57..0f40c14 100644
--- a/runtime/observatory/lib/src/elements/timeline/dashboard.dart
+++ b/runtime/observatory/lib/src/elements/timeline/dashboard.dart
@@ -97,7 +97,7 @@
     _frame.src = _makeFrameUrl();
     _content.children = [
       new HeadingElement.h2()
-        ..children = ([new Text("Timeline View")]
+        ..nodes = ([new Text("Timeline View")]
           ..addAll(_createButtons())
           ..addAll(_createTabs())),
       new ParagraphElement()
@@ -118,7 +118,7 @@
     }
   }
 
-  List<Element> _createButtons() {
+  List<Node> _createButtons() {
     if (_flags == null) {
       return [new Text('Loading')];
     }