Support subtitles for native fullscreen video

Source/core/rendering/RenderLayerCompositor.h

Index: Source/core/rendering/RenderLayerCompositor.h
diff --git a/Source/core/rendering/RenderLayerCompositor.h b/Source/core/rendering/RenderLayerCompositor.h
index ac4edaee3a3e758ee01301bffec76567d96a5f79..ed6e8c18af96ab57f3bc5a66ac6f4c0cfc1766b2 100644
--- a/Source/core/rendering/RenderLayerCompositor.h
+++ b/Source/core/rendering/RenderLayerCompositor.h
@@ -205,6 +205,9 @@ public:
     // Returns all reasons (direct, indirectly due to subtree, and indirectly due to overlap) that a layer should be composited.
     CompositingReasons reasonsForCompositing(const RenderLayer*) const;
 
+    // Only called for main frame. Input object can be cross frame.
+    void setCurrentFullscreenRenderer(RenderObject*);
+
 private:
     class OverlapMap;
 
@@ -350,6 +353,8 @@ private:
     OwnPtr<GraphicsLayer> m_layerForOverhangAreas;
 #endif
 
+    RenderObject* m_currentFullscreenRenderer;
+
 #if !LOG_DISABLED
     int m_rootLayerUpdateCount;
     int m_obligateCompositedLayerCount; // count of layer that have to be composited.