dart2js: fix a few TODOs in the startup emitter.

pkg/compiler/lib/src/js_emitter/full_emitter/emitter.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 dart2js.js_emitter.full_emitter;
 
 import 'dart:convert';
 import 'dart:collection' show HashMap;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
@@ skipping 830 matching lines @@
   buildMain(jsAst.Statement invokeMain) {
     if (compiler.isMockCompilation) return js.comment("Mock compilation");
 
     List<jsAst.Statement> parts = <jsAst.Statement>[];
 
     if (NativeGenerator.needsIsolateAffinityTagInitialization(backend)) {
       parts.add(
           NativeGenerator.generateIsolateAffinityTagInitialization(
               backend,
               generateEmbeddedGlobalAccess,
-              js("convertToFastObject", [])));
+              js("""
+        // On V8, the 'intern' function converts a string to a symbol, which
+        // makes property access much faster.
+        function (s) {
+          var o = {};
+          o[s] = 1;
+          return Object.keys(convertToFastObject(o))[0];
+        }""", [])));
     }
 
     parts..add(js.comment('BEGIN invoke [main].'))
          ..add(invokeMain)
          ..add(js.comment('END invoke [main].'));
 
     return new jsAst.Block(parts);
   }
 
   jsAst.Statement buildInitFunction(bool outputContainsConstantList) {
@@ skipping 1245 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }