isolates refactor: this change introduces 'dart:isolate' as a library. This is a

lib/isolate/frog/compiler_hooks.dart

Index: lib/isolate/frog/compiler_hooks.dart
diff --git a/lib/isolate/frog/compiler_hooks.dart b/lib/isolate/frog/compiler_hooks.dart
new file mode 100644
index 0000000000000000000000000000000000000000..31f4d80eb61739f3b71a5ea92790c0e0c0ed2518
--- /dev/null
+++ b/lib/isolate/frog/compiler_hooks.dart
@@ -0,0 +1,31 @@
+// 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 frog
+// compiler.
+
+/**
+ * Wrapper that takes the dart entry point and runs it within an isolate. The
+ * frog 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 GlobalState();
+
+  // 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;
+
+  rootContext.eval(entry);
+  globalState.topEventLoop.run();
+}