Redo "dart2js: --fast-startup: use alias for 'this'"

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.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.js_emitter.startup_emitter.model_emitter;
 
 import 'dart:convert' show JsonEncoder;
 
 import 'package:js_runtime/shared/embedded_names.dart'
     show
@@ skipping 24 matching lines @@
 import '../../compiler.dart' show Compiler;
 import '../../constants/values.dart' show ConstantValue, FunctionConstantValue;
 import '../../common_elements.dart' show CommonElements;
 import '../../elements/elements.dart' show ClassElement, MethodElement;
 import '../../hash/sha1.dart' show Hasher;
 import '../../io/code_output.dart';
 import '../../io/location_provider.dart' show LocationCollector;
 import '../../io/source_map_builder.dart' show SourceMapBuilder;
 import '../../js/js.dart' as js;
 import '../../js_backend/js_backend.dart'
-    show JavaScriptBackend, Namer, ConstantEmitter;
+    show JavaScriptBackend, Namer, ConstantEmitter, StringBackedName;
 import '../constant_ordering.dart' show deepCompareConstants;
 import '../headers.dart';
 import '../js_emitter.dart' show NativeEmitter;
 import '../js_emitter.dart' show buildTearOffCode, NativeGenerator;
 import '../model.dart';
 
 part 'deferred_fragment_hash.dart';
 part 'fragment_emitter.dart';
 
 class ModelEmitter {
@@ skipping 322 matching lines @@
     // data.
     mapping["_comment"] = "This mapping shows which compiled `.js` files are "
         "needed for a given deferred library import.";
     mapping.addAll(compiler.deferredLoadTask.computeDeferredMap());
     compiler.outputProvider(
         compiler.options.deferredMapUri.path, '', OutputType.info)
       ..add(const JsonEncoder.withIndent("  ").convert(mapping))
       ..close();
   }
 }