anchor.diff:    }
   
     Future<T> _runWithFrontEndContext<T>(String msg, Future<T> f()) async {
  -    // TODO(brianwilkerson) Determine whether this await is necessary.
  -    await null;
       return await CompilerContext.runWithOptions(_options, (context) {
         context.disableColors();
         return _logger.runAsync(msg, f);
  
positive.code:     }
  
      return _runWithFrontEndContext('Compile', () async {
        // TODO(brianwilkerson) Determine whether this await is necessary.
        await null;
        try {
          var dillTarget =
              new DillTarget(_options.ticker, uriTranslator, _options.target);
  
          // Append all libraries what we still have in the current component.
          await _logger.runAsync('Load dill libraries', () async {
            // TODO(brianwilkerson) Determine whether this await is necessary.
            await null;
            dillTarget.loader.appendLibraries(_component);
            await dillTarget.buildOutlines();
          });
  
          // Create the target to compile the library.
          var kernelTarget = new _AnalyzerKernelTarget(_fileSystem, dillTarget,
              uriTranslator, new AnalyzerMetadataCollector());
          kernelTarget.read(uri);
  
  
negative.code:   /// we remove the file, its library, and everything affected from [_component].
    Component _component = new Component();
  
    /// The [DillTarget] that is filled with [_component] libraries before
    /// compilation of a new library.
    DillTarget _dillTarget;
  
    /// Each key is the file system URI of a library.
    /// Each value is the libraries that directly depend on the key library.
    final Map<Uri, Set<Uri>> _directLibraryDependencies = {};
  