Uncomment and clean up engine_test.dart

pkg/analyzer/test/generated/test_support.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.test_support;
 
 import 'dart:collection';
@@ skipping 939 matching lines @@
   @override
   void logInformation2(String message, Exception exception) {
     infoCount++;
   }
 }
 
 
 class TestSource implements Source {
   String _name;
   String _contents;
+  int modificationStamp = 0;
+  bool exists2 = true;
+
+  /**
+   * A flag indicating whether an exception should be generated when an attempt
+   * is made to access the contents of this source.
+   */
+  bool generateExceptionOnRead = false;
+
+  /**
+   * The number of times that the contents of this source have been requested.
+   */
+  int readCount = 0;
+
   TestSource([this._name = '/test.dart', this._contents]);
+
   TimestampedData<String> get contents {
+    readCount++;
+    if (generateExceptionOnRead) {
+      throw new Exception("I/O Exception while getting the contents of " + _name);
+    }
     return new TimestampedData<String>(0, _contents);
   }
+  void setContents(String value) {
+    modificationStamp = new DateTime.now().millisecondsSinceEpoch;
+    _contents = value;
+  }
   String get encoding {
     throw new UnsupportedOperationException();
   }
   String get fullName {
     return _name;
   }
   int get hashCode => 0;
   bool get isInSystemLibrary {
     return false;
   }
-  int get modificationStamp {
-    return 0;
-  }
   String get shortName {
     return _name;
   }
   Uri get uri {
     throw new UnsupportedOperationException();
   }
   UriKind get uriKind {
     throw new UnsupportedOperationException();
   }
-  bool operator ==(Object object) {
-    return object is TestSource;
+  bool operator ==(Object other) {
+    if (other is TestSource) {
+      return other._name == _name;
+    }
+    return false;
   }
-  bool exists() => true;
+  bool exists() => exists2;
   void getContentsToReceiver(Source_ContentReceiver receiver) {
     throw new UnsupportedOperationException();
   }
   Source resolve(String uri) {
     throw new UnsupportedOperationException();
   }
   Uri resolveRelativeUri(Uri uri) {
     return new Uri(scheme: 'file', path: _name).resolveUri(uri);
   }
 }