compositor-worker: Introduce CompositorWorker.

Source/modules/compositorworker/CompositorWorker.idl

Index: Source/modules/compositorworker/CompositorWorker.idl
diff --git a/Source/modules/compositorworker/CompositorWorker.idl b/Source/modules/compositorworker/CompositorWorker.idl
new file mode 100644
index 0000000000000000000000000000000000000000..932be419ce0babd5d40091715dc96993dd965430
--- /dev/null
+++ b/Source/modules/compositorworker/CompositorWorker.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.
+
+[
+    ActiveDOMObject,
+    Constructor(DOMString scriptUrl),
+    ConstructorCallWith=ExecutionContext,
+    RaisesException=Constructor,
+    RuntimeEnabled=CompositorWorker,
+    WillBeGarbageCollected,
+] interface CompositorWorker : Worker {
+};