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..57cfb019ad4d6193bec22110c4bb581019dfdee1 100644
--- a/Source/core/platform/graphics/GraphicsLayer.cpp
+++ b/Source/core/platform/graphics/GraphicsLayer.cpp
@@ -1069,6 +1069,11 @@ int GraphicsLayer::debugID() const
     return m_layer ? m_layer->layer()->id() : DebugIDNoCompositedLayer;
 }
 
+void GraphicsLayer::setCompositingReasons(WebKit::WebCompositingReasons reasons)
+{
+    m_layer->layer()->setCompositingReasons(reasons);
+}
+
 void GraphicsLayer::setPosition(const FloatPoint& point)
 {
     m_position = point;