compositor-worker: Introduce CompositorWorker.

Source/modules/compositorworker/CompositorWorkerGlobalScope.idl

Index: Source/modules/compositorworker/CompositorWorkerGlobalScope.idl
diff --git a/Source/modules/compositorworker/CompositorWorkerGlobalScope.idl b/Source/modules/compositorworker/CompositorWorkerGlobalScope.idl
new file mode 100644
index 0000000000000000000000000000000000000000..bcb8410c0fba9f9e49e67f1f1a9e3b4c4f7d3fb4
--- /dev/null
+++ b/Source/modules/compositorworker/CompositorWorkerGlobalScope.idl
@@ -0,0 +1,13 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+[
+    Exposed=CompositorWorker,
+    Global=(Worker,CompositorWorker),
+    RuntimeEnabled=CompositorWorker,
+    TypeChecking=Interface,
+] interface CompositorWorkerGlobalScope : WorkerGlobalScope {
+    [Custom, RaisesException] void postMessage(any message, optional sequence<Transferable> transfer);
+    attribute EventHandler onmessage;
+};