Plumb CompositingReason from Blink to compositor.

Source/core/platform/graphics/GraphicsLayer.h

Index: Source/core/platform/graphics/GraphicsLayer.h
diff --git a/Source/core/platform/graphics/GraphicsLayer.h b/Source/core/platform/graphics/GraphicsLayer.h
index 621578d199caed83e222669ad9293d63a3625322..938da0865a38637cfc742888e058ca9b4f97092a 100644
--- a/Source/core/platform/graphics/GraphicsLayer.h
+++ b/Source/core/platform/graphics/GraphicsLayer.h
@@ -43,6 +43,7 @@
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 
+#include <public/WebCompositingReasons.h>
 #include <public/WebContentLayer.h>
 #include <public/WebImageLayer.h>
 #include <public/WebLayer.h>
@@ -232,6 +233,8 @@ public:
     // Layer ID from platform-specific layer. Only used to identify layers in the compositor for debugging purposes.
     int debugID() const;
 
+    void setCompositingReasons(WebKit::WebCompositingReasons);
+
     GraphicsLayer* parent() const { return m_parent; };
     void setParent(GraphicsLayer*); // Internal use only.