Plumb CompositingReason from Blink to compositor.

Source/core/platform/graphics/GraphicsLayer.cpp

Index: Source/core/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/core/platform/graphics/GraphicsLayer.cpp b/Source/core/platform/graphics/GraphicsLayer.cpp
index cbccc1fcbe8a114eaf10eb1a49a2ce8c274992f3..c990e0d55c3c1586b49c5801c0f42ff6f414b757 100644
--- a/Source/core/platform/graphics/GraphicsLayer.cpp
+++ b/Source/core/platform/graphics/GraphicsLayer.cpp
@@ -55,6 +55,7 @@
 
 #include <public/Platform.h>
 #include <public/WebAnimation.h>
+#include <public/WebCompositingReasons.h>
 #include <public/WebCompositorSupport.h>
 #include <public/WebFilterOperation.h>
 #include <public/WebFilterOperations.h>
@@ -1069,6 +1070,12 @@ int GraphicsLayer::debugID() const
     return m_layer ? m_layer->layer()->id() : DebugIDNoCompositedLayer;
 }
 
+void GraphicsLayer::setCompositingReasons(CompositingReasons reasons)
+{
+    WebKit::WebCompositingReasons webReasons = reasons;
+    m_layer->layer()->setCompositingReasons(webReasons);
+}
+
 void GraphicsLayer::setPosition(const FloatPoint& point)
 {
     m_position = point;