Move iframe and plugin compositing triggers into additionalCompositingReasons

Source/core/rendering/RenderEmbeddedObject.h

Index: Source/core/rendering/RenderEmbeddedObject.h
diff --git a/Source/core/rendering/RenderEmbeddedObject.h b/Source/core/rendering/RenderEmbeddedObject.h
index 3ef8f625b70f19d93d171bfbe3381e1d8e87b820..f6c5a48aaee7815b791c282676910e307801d8bd 100644
--- a/Source/core/rendering/RenderEmbeddedObject.h
+++ b/Source/core/rendering/RenderEmbeddedObject.h
@@ -75,6 +75,8 @@ private:
     virtual RenderObjectChildList* virtualChildren() OVERRIDE FINAL { return children(); }
     virtual const RenderObjectChildList* virtualChildren() const OVERRIDE FINAL { return children(); }
 
+    virtual CompositingReasons additionalCompositingReasons(CompositingTriggerFlags) const OVERRIDE;
+
     bool m_hasFallbackContent; // FIXME: This belongs on HTMLObjectElement.
 
     bool m_showsUnavailablePluginIndicator;