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 ed05dc6d2ac29e09aa60a9e01c70d95a9ca3e209..e95dc73468be91a0e9e3e1fea34c2d4fb023a7f2 100644
--- a/Source/core/rendering/RenderLayerCompositor.h
+++ b/Source/core/rendering/RenderLayerCompositor.h
@@ -206,6 +206,9 @@ public:
 
     virtual String debugName(const GraphicsLayer*) OVERRIDE;
 
+    // Only called for main frame. Input object can be cross frame.
+    void setCurrentFullscreenRenderer(RenderObject*);
+
 private:
     class OverlapMap;
 
@@ -354,6 +357,8 @@ private:
     OwnPtr<GraphicsLayer> m_layerForOverhangShadow;
 #endif
 
+    RenderObject* m_currentFullscreenRenderer;
+
 #if !LOG_DISABLED
     int m_rootLayerUpdateCount;
     int m_obligateCompositedLayerCount; // count of layer that have to be composited.