Replace Backend with JavaScriptBackend.

pkg/compiler/lib/src/parser/diet_parser_task.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 dart2js.parser.diet.task;
 
 import '../common.dart';
-import '../common/backend_api.dart' show Backend;
 import '../common/tasks.dart' show CompilerTask, Measurer;
 import '../elements/elements.dart' show CompilationUnitElement;
+import '../js_backend/backend.dart' show JavaScriptBackend;
 import '../id_generator.dart';
 import 'package:front_end/src/fasta/scanner.dart' show Token;
 import 'element_listener.dart' show ElementListener, ScannerOptions;
 import 'package:front_end/src/fasta/parser.dart'
     show Listener, ParserError, TopLevelParser;
 
 class PartialParser extends TopLevelParser {
   PartialParser(Listener listener) : super(listener);
 
   Token parseFormalParameters(Token token) => skipFormalParameters(token);
 }
 
 class DietParserTask extends CompilerTask {
   final IdGenerator _idGenerator;
-  final Backend _backend;
+  final JavaScriptBackend _backend;
   final DiagnosticReporter _reporter;
 
   DietParserTask(
       this._idGenerator, this._backend, this._reporter, Measurer measurer)
       : super(measurer);
 
   final String name = 'Diet Parser';
 
   dietParse(CompilationUnitElement compilationUnit, Token tokens) {
     measure(() {
       ScannerOptions scannerOptions = new ScannerOptions(
           canUseNative: _backend.canLibraryUseNative(compilationUnit.library));
       ElementListener listener = new ElementListener(
           scannerOptions, _reporter, compilationUnit, _idGenerator);
       PartialParser parser = new PartialParser(listener);
       try {
         parser.parseUnit(tokens);
       } on ParserError catch (_) {
         // TODO(johnniwinther): assert that the error was reported once there is
         // a [hasErrorBeenReported] field in [DiagnosticReporter]
         // The error should have already been reported by the parser.
       }
     });
   }
 }