fixes #221, initial sync*, async, async* implementation

test/testing.dart

 // Copyright (c) 2015, 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 dev_compiler.src.testing;
 
 import 'dart:mirrors';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 11 matching lines @@
 import 'package:dev_compiler/src/analysis_context.dart';
 
 import 'package:dev_compiler/src/server/dependency_graph.dart'
     show runtimeFilesForServerMode;
 import 'package:dev_compiler/src/info.dart';
 import 'package:dev_compiler/src/options.dart';
 import 'package:dev_compiler/src/utils.dart';
 
 /// Shared analysis context used for compilation.
 final realSdkContext = createAnalysisContextWithSources(new StrongModeOptions(),
-    new SourceResolverOptions(dartSdkPath: getSdkDir().path))
-  ..analysisOptions = (new AnalysisOptionsImpl()..cacheSize = 512);
+    new SourceResolverOptions(
+        dartSdkPath: getSdkDir().path,
+        customUrlMappings: {
+  'package:expect/expect.dart': _testCodegenPath('expect.dart'),
+  'package:async_helper/async_helper.dart':
+      _testCodegenPath('async_helper.dart'),
+  'package:unittest/unittest.dart': _testCodegenPath('unittest.dart'),
+  'package:dom/dom.dart': _testCodegenPath('sunflower', 'dom.dart')
+}))..analysisOptions = (new AnalysisOptionsImpl()..cacheSize = 512);
+
+String _testCodegenPath(String p1, [String p2]) =>
+    path.join(testDirectory, 'codegen', p1, p2);
 
 final String testDirectory =
     path.dirname((reflectClass(_TestUtils).owner as LibraryMirror).uri.path);
 
 class _TestUtils {}
 
 /// Run the checker on a program with files contents as indicated in
 /// [testFiles].
 ///
 /// This function makes several assumptions to make it easier to describe error
@@ skipping 214 matching lines @@
     expect(tokens[1], "should", reason: 'invalid error descriptor');
     expect(tokens[2], "be", reason: 'invalid error descriptor');
     if (tokens[0] == "pass") return null;
     // TODO(leafp) For now, we just use whatever the current expectation is,
     // eventually we could do more automated reporting here.
     return _parse(tokens[0]);
   }
 
   String toString() => '$level $typeName';
 }