Bug 1079755 - Send composer info to Layerscope viewer. r=kamidphish

Add a composition info, composedByHwc, in META packet to
notify users whether this frame is composed by Hardware composer.

gfx/layers/LayerScope.h

@@ -1,4 +1,5 @@
-/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* vim:set ts=4 sw=4 sts=4 et: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
@@ -34,6 +35,7 @@ public:
     static void SendLayerDump(UniquePtr<layerscope::Packet> aPacket);
     static bool CheckSendable();
     static void CleanLayer();
+    static void SetHWComposed();
 
 private:
     static void Init();