Improve strong-mode implementation and fix several failing tests

pkg/analyzer/lib/src/generated/engine.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 library engine;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
@@ skipping 8397 matching lines @@
       DartEntry dartEntry = sourceEntry;
       if (astIsNeeded(dartEntry)) {
         return RetentionPriority.MEDIUM;
       }
     }
     return RetentionPriority.LOW;
   }
 }
 
 /**
+ * An error listener that can be enabled or disabled while executing a function.
+ */
+class DisablableErrorListener implements AnalysisErrorListener {

[scheglov, 2015/09/08 15:36:22]

Why don't we put it in error.dart ?

[Brian Wilkerson, 2015/09/08 17:10:33]

Done

+  /**
+   * The listener to which errors will be reported if this listener is enabled.
+   */
+  final AnalysisErrorListener baseListener;
+
+  /**
+   * A flag indicating whether this listener is currently enabled.
+   */
+  bool enabled = true;
+
+  /**
+   * Initialize a newly created listener to report errors to the given
+   * [baseListener].
+   */
+  DisablableErrorListener(this.baseListener);
+
+  /**
+   * Disable the processing of errors while evaluating the given [function].
+   * Return the value returned by the function.
+   */
+  dynamic disableWhile(dynamic function()) {
+    bool wasEnabled = enabled;
+    try {
+      enabled = false;
+      return function();
+    } finally {
+      enabled = wasEnabled;
+    }
+  }
+
+  /**
+   * Disable the processing of errors while evaluating the given [function].
+   * Return the value returned by the function.
+   */
+  dynamic enableWhile(dynamic function()) {
+    bool wasEnabled = enabled;
+    try {
+      enabled = true;
+      return function();
+    } finally {
+      enabled = wasEnabled;
+    }
+  }
+
+  @override
+  void onError(AnalysisError error) {
+    if (enabled) {
+      baseListener.onError(error);
+    }
+  }
+}
+
+/**
  * Instances of the class `GenerateDartErrorsTask` generate errors and warnings for a single
  * Dart source.
  */
 class GenerateDartErrorsTask extends AnalysisTask {
   /**
    * The source for which errors and warnings are to be produced.
    */
   final Source source;
 
   /**
@@ skipping 3606 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, source, computeValue);
     if (!pendingFuture.evaluate(sourceEntry)) {
       _context._pendingFutureSources
           .putIfAbsent(source, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }