Re-apply 'Unify dart:isolate.' with fixes for autogenerated dart2js and dartium html files.

lib/isolate/isolate_compiler.dart

-// Copyright (c) 2012, 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.
-
-
-// Dart isolate's API for the dartc compiler (only used for type checking in the
-// dart editor, but not for code generation).
-#library("dart:isolate");
-
-#source("isolate_api.dart");
-#source("timer.dart");
-#source("timer_hook.dart");
-
-SendPort _spawnFunction(void topLevelFunction()) {
-  throw new NotImplementedException();
-}
-
-SendPort _spawnUri(String uri) {
-  throw new NotImplementedException();
-}
-
-ReceivePort _port = null;
-
-class _ReceivePortFactory {
-  factory ReceivePort() {
-    throw new NotImplementedException();
-  }
-}