anchor.diff:    DartUriResolverProxy(DirectoryBasedDartSdk sdk) :
         _proxy = new DartUriResolver(sdk);
   
  -  Source resolveAbsolute(ContentCache contentCache, Uri uri) =>
  -    _DartSourceProxy.wrap(_proxy.resolveAbsolute(contentCache, uri), uri);
  +  Source resolveAbsolute(Uri uri) =>
  +    _DartSourceProxy.wrap(_proxy.resolveAbsolute(uri), uri);
   
     DartSdk get dartSdk => _proxy.dartSdk;
   
  -  Source fromEncoding(ContentCache contentCache, UriKind kind, Uri uri) =>
  +  Source fromEncoding(UriKind kind, Uri uri) =>
         throw new UnsupportedError('fromEncoding is not supported');
   
     Uri restoreAbsolute(Source source) =>
  
positive.code:     var sourceFile = _getSourceFile(element);
      if (sourceFile == null) return null;
  
      return new TextEditTransaction(source.contents, sourceFile);
    }
  
    /// Gets the SourceFile for the source of the element.
  
negative.code:     return source;
    }
  
    Source fromEncoding(UriKind kind, Uri uri) =>
        throw new UnsupportedError('fromEncoding is not supported');
  
    Uri restoreAbsolute(Source source) =>
  