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

lib/isolate/dart2js/compiler_hooks.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.
-
-// This file contains functions that are used in the code generated by
-// the dart2js compiler.
-
-/**
- * Wrapper that takes the dart entry point and runs it within an isolate. The
- * dart2js compiler will inject a call of the form
- * [: startRootIsolate(main); :] when it determines that this wrapping
- * is needed. For single-isolate applications (e.g. hello world), this
- * call is not emitted.
- */
-void startRootIsolate(entry) {
-  _globalState = new _Manager();
-
-  // Don't start the main loop again, if we are in a worker.
-  if (_globalState.isWorker) return;
-  final rootContext = new _IsolateContext();
-  _globalState.rootContext = rootContext;
-  _fillStatics(rootContext);
-
-  // BUG(5151491): Setting currentContext should not be necessary, but
-  // because closures passed to the DOM as event handlers do not bind their
-  // isolate automatically we try to give them a reasonable context to live in
-  // by having a "default" isolate (the first one created).
-  _globalState.currentContext = rootContext;
-
-  if (_window != null)  {
-    rootContext.eval(() => _setTimerFactoryClosure( _timerFactory));
-  }
-  rootContext.eval(entry);
-  _globalState.topEventLoop.run();
-}