patch from issue 428303004

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 90 matching lines @@
   final Source _proxy;
 
   DartSourceProxy(this._proxy, this.uri);
 
   /// Ensures that [source] is a DartSourceProxy.
   static DartSourceProxy wrap(Source source, Uri uri) {
     if (source == null || source is DartSourceProxy) return source;
     return new DartSourceProxy(source, uri);
   }
 
-  Source resolveRelative(Uri relativeUri) {
-    // Assume that the type can be accessed via this URI, since these
-    // should only be parts for dart core files.
-    return wrap(_proxy.resolveRelative(relativeUri), uri);
-  }
+  Uri resolveRelative(Uri relativeUri) => _proxy.resolveRelative(relativeUri);
 
   bool exists() => _proxy.exists();
 
   bool operator ==(Object other) =>
     (other is DartSourceProxy && _proxy == other._proxy);
 
   int get hashCode => _proxy.hashCode;
 
   TimestampedData<String> get contents => _proxy.contents;
 
@@ skipping 48 matching lines @@
 
   Source _getSource(Uri uri) {
     var src = _sources[uri];
     if (src == null) {
       if (reportMissing) print('warning: missing mock for $uri.');
       _sources[uri] = src =
           new _MockSdkSource(uri, 'library dart.${uri.path};');
     }
     return src;
   }
+
+  @override
+  Source fromFileUri(Uri uri) {
+    throw new UnsupportedError('MockDartSdk.fromFileUri');
+  }
 }
 
 class _MockSdkSource implements UriAnnotatedSource {
   /// Absolute URI which this source can be imported from.
   final Uri uri;
   final String _contents;
 
   _MockSdkSource(this.uri, this._contents);
 
   bool exists() => true;
 
   int get hashCode => uri.hashCode;
 
   final int modificationStamp = 1;
 
   TimestampedData<String> get contents =>
       new TimestampedData(modificationStamp, _contents);
 
   String get encoding => "${uriKind.encoding}$uri";
 
   String get fullName => shortName;
 
   String get shortName => uri.path;
 
   UriKind get uriKind => UriKind.DART_URI;
 
   bool get isInSystemLibrary => true;
 
-  Source resolveRelative(Uri relativeUri) =>
+  Uri resolveRelative(Uri relativeUri) =>
       throw new UnsupportedError('not expecting relative urls in dart: mocks');
 }