Plumb CompositingReason from Blink to compositor.

Source/Platform/Platform.gypi

 #
 # Copyright (C) 2011 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #         * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #         * Redistributions in binary form must reproduce the above
@@ skipping 26 matching lines @@
             'chromium/public/WebAnimationDelegate.h',
             'chromium/public/WebAudioBus.h',
             'chromium/public/WebAudioDevice.h',
             'chromium/public/WebBlobData.h',
             'chromium/public/WebBlobRegistry.h',
             'chromium/public/WebCString.h',
             'chromium/public/WebCanvas.h',
             'chromium/public/WebClipboard.h',
             'chromium/public/WebColor.h',
             'chromium/public/WebCommon.h',
+            'chromium/public/WebCompositingReasons.h',
             'chromium/public/WebCompositorSupport.h',
             'chromium/public/WebCompositorOutputSurface.h',
             'chromium/public/WebContentLayer.h',
             'chromium/public/WebContentLayerClient.h',
             'chromium/public/WebCookie.h',
             'chromium/public/WebCookieJar.h',
             'chromium/public/WebCursorInfo.h',
             'chromium/public/WebData.h',
             'chromium/public/WebDiscardableMemory.h',
             'chromium/public/WebDragData.h',
@@ skipping 117 matching lines @@
             'chromium/public/linux/WebFontInfo.h',
             'chromium/public/linux/WebFontRenderStyle.h',
             'chromium/public/linux/WebSandboxSupport.h',
             'chromium/public/mac/WebSandboxSupport.h',
             'chromium/public/mac/WebThemeEngine.h',
             'chromium/public/win/WebSandboxSupport.h',
             'chromium/public/win/WebThemeEngine.h',
         ]
     }
 }