Fix bug in code_transformers. Apparently mock SDK needs to have a source factory

pkg/code_transformers/lib/src/dart_sdk.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 code_transformers.src.dart_sdk;
 
 import 'dart:convert' as convert;
 import 'dart:io' show File, Platform, Process;
 import 'package:path/path.dart' as path;
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 128 matching lines @@
 
 /// Dart SDK which contains a mock implementation of the SDK libraries. May be
 /// used to speed up resultion when most of the core libraries is not needed.
 class MockDartSdk implements DartSdk {
   final Map<Uri, _MockSdkSource> _sources = {};
   final bool reportMissing;
   final Map<String, SdkLibrary> _libs = {};
   final String sdkVersion = '0';
   List<String> get uris => _sources.keys.map((uri) => '$uri').toList();
   final AnalysisContext context = new _SdkAnalysisContext();
+  DartUriResolver _resolver;
+  DartUriResolver get resolver => _resolver;
 
   MockDartSdk(Map<String, String> sources, {this.reportMissing}) {
     sources.forEach((uriString, contents) {
       var uri = Uri.parse(uriString);
       _sources[uri] = new _MockSdkSource(uri, contents);
       _libs[uriString] = new SdkLibraryImpl(uri.path)
         ..setDart2JsLibrary()
         ..setVmLibrary();
     });
+    _resolver = new DartUriResolver(this);
+    context.sourceFactory = new SourceFactory([_resolver]);
   }
 
   List<SdkLibrary> get sdkLibraries => _libs.values.toList();
   SdkLibrary getSdkLibrary(String dartUri) => _libs[dartUri];
   Source mapDartUri(String dartUri) => _getSource(Uri.parse(dartUri));
 
   Source fromEncoding(UriKind kind, Uri uri) {
     if (kind != UriKind.DART_URI) {
       throw new UnsupportedError('expected dart: uri kind, got $kind.');
     }
@@ skipping 48 matching lines @@
 class _SdkAnalysisContext extends AnalysisContextImpl {
   @override
   AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
     if (factory == null) return super.createCacheFromSourceFactory(factory);
     var sdk = factory.dartSdk;
     if (sdk == null) throw "Missing a DartUriResolver in source factory";
     return new AnalysisCache(
         [AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }