Improve execution context logging (#1206)

diff --git a/dwds/CHANGELOG.md b/dwds/CHANGELOG.md
index 3270d20..5d61945 100644
--- a/dwds/CHANGELOG.md
+++ b/dwds/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 7.1.2 - UNRELEASED
+
+- Improve logging around execution contexts.
+
 ## 7.1.1
 
 - Properly handle `requireJS` errors during hot restarts.
diff --git a/dwds/lib/src/debugging/execution_context.dart b/dwds/lib/src/debugging/execution_context.dart
index 57bb115..8bc1b26 100644
--- a/dwds/lib/src/debugging/execution_context.dart
+++ b/dwds/lib/src/debugging/execution_context.dart
@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:async/async.dart';
+import 'package:logging/logging.dart';
 
 import 'remote_debugger.dart';
 
@@ -16,6 +17,7 @@
 /// The execution context in which to do remote evaluations.
 class RemoteDebuggerExecutionContext extends ExecutionContext {
   final RemoteDebugger _remoteDebugger;
+  final _logger = Logger('RemoteDebuggerExecutionContext');
 
   // Contexts that may contain a Dart application.
   StreamQueue<int> _contexts;
@@ -25,9 +27,11 @@
   @override
   Future<int> get id async {
     if (_id != null) return _id;
+    _logger.fine('Looking for Dart execution context...');
     while (await _contexts.hasNext
         .timeout(const Duration(milliseconds: 50), onTimeout: () => false)) {
       var context = await _contexts.next;
+      _logger.fine('Checking context id: $context');
       try {
         var result =
             await _remoteDebugger.sendCommand('Runtime.evaluate', params: {
@@ -35,12 +39,14 @@
           'contextId': context,
         });
         if (result.result['result']['value'] != null) {
+          _logger.fine('Found valid execution context: $context');
           _id = context;
           break;
         }
       } catch (_) {
         // Errors may be thrown if we attempt to evaluate in a stale a context.
         // Ignore and continue.
+        _logger.fine('Invalid execution context: $context');
       }
     }
     if (_id == null) {
diff --git a/dwds/lib/src/version.dart b/dwds/lib/src/version.dart
index 5d7be62..4919dd0 100644
--- a/dwds/lib/src/version.dart
+++ b/dwds/lib/src/version.dart
@@ -1,2 +1,2 @@
 // Generated code. Do not modify.
-const packageVersion = '7.1.1';
+const packageVersion = '7.1.2';
diff --git a/dwds/pubspec.yaml b/dwds/pubspec.yaml
index aebbdc6..c1055d0 100644
--- a/dwds/pubspec.yaml
+++ b/dwds/pubspec.yaml
@@ -1,6 +1,6 @@
 name: dwds
 # Every time this changes you need to run `pub run build_runner build`.
-version: 7.1.1
+version: 7.1.2
 homepage: https://github.com/dart-lang/webdev/tree/master/dwds
 description: >-
   A service that proxies between the Chrome debug protocol and the Dart VM
diff --git a/frontend_server_common/lib/src/asset_server.dart b/frontend_server_common/lib/src/asset_server.dart
index 262801f..2d61908 100644
--- a/frontend_server_common/lib/src/asset_server.dart
+++ b/frontend_server_common/lib/src/asset_server.dart
@@ -17,7 +17,6 @@
 import 'package:package_config/packages.dart'; // ignore: deprecated_member_use
 import 'package:path/path.dart' as p;
 import 'package:shelf/shelf.dart' as shelf;
-import 'package:shelf/shelf_io.dart' as shelf;
 
 import 'utilities.dart';