Fix equality between subclasses of Source

pkg/analyzer/test/src/context/context_test.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 analyzer.test.src.context.context_test;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2420 matching lines @@
     ChangeSet changeSet = new ChangeSet();
     changeSet.addedSource(source);
     context.applyChanges(changeSet);
     return source;
   }
 
   /**
    * Perform analysis tasks up to 512 times and assert that it was enough.
    */
   void _analyzeAll_assertFinished([int maxIterations = 512]) {
+    bool finishedAnalyzing = false;
     for (int i = 0; i < maxIterations; i++) {
       List<ChangeNotice> notice = context.performAnalysisTask().changeNotices;
       if (notice == null) {
+        finishedAnalyzing = true;
         bool inconsistent = context.validateCacheConsistency();
         if (!inconsistent) {
           return;
         }
       }
     }
-    fail("performAnalysisTask failed to terminate after analyzing all sources");
+    if (finishedAnalyzing) {
+      fail(
+          "performAnalysisTask failed to finish analyzing all sources after $maxIterations iterations");
+    } else {
+      fail(
+          "performAnalysisTask failed to terminate after analyzing all sources");
+    }
   }
 
   void _assertNoExceptions() {
     MapIterator<AnalysisTarget, CacheEntry> iterator = analysisCache.iterator();
     String exceptionsStr = '';
     while (iterator.moveNext()) {
       CaughtException exception = iterator.value.exception;
       if (exception != null) {
         AnalysisTarget target = iterator.key;
         exceptionsStr +=
@@ skipping 483 matching lines @@
    * Initialize the visitor.
    */
   _ElementGatherer();
 
   @override
   void visitElement(Element element) {
     elements[element] = element;
     super.visitElement(element);
   }
 }