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

lib/isolate/isolate_frog.dart

+// Copyright (c) 2011, 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 and implementation for frog.
+#library("dart:isolate");
+
+#import("frog/isolateimpl.dart");
+#import("frog/ports.dart");
+
+#source("isolate_api.dart");
+#source("frog/compiler_hooks.dart");
+
+/** Default factory for [Isolate2]. */
+class _IsolateFactory {
+
+  factory Isolate2.fromCode(Function topLevelFunction) {
+    final name = IsolateNatives._getJSFunctionName(topLevelFunction);
+    if (name == null) {
+      throw new UnsupportedOperationException(
+          "only top-level functions can be spawned.");
+    }
+    return new Isolate2Impl(IsolateNatives._spawn2(name, null, false));
+  }
+
+  factory Isolate2.fromUri(String uri) {
+    return new Isolate2Impl(IsolateNatives._spawn2(null, uri, false));
+  }
+}
+
+class _IsolateNatives {
+  static Future<SendPort> spawn(Isolate isolate, bool isLight) {
+    return IsolateNatives.spawn(isolate, isLight);
+  }
+}