Let the WebMediaPlayer decide whether to use overlay video.

public/platform/WebMediaPlayer.h

Index: public/platform/WebMediaPlayer.h
diff --git a/public/platform/WebMediaPlayer.h b/public/platform/WebMediaPlayer.h
index e9f7a60c782d73335f55d7520ca3591e47dbf01a..c7f0a013304e2abec4af4084a45cf4b5afd61f37 100644
--- a/public/platform/WebMediaPlayer.h
+++ b/public/platform/WebMediaPlayer.h
@@ -176,6 +176,11 @@ public:
     // Sets the poster image URL.
     virtual void setPoster(const WebURL& poster) { }
 
+    // Whether the WebMediaPlayer supports overlay fullscreen video mode. When
+    // this is true, the video layer will be removed from the layer tree when
+    // entering fullscreen, and the WebMediaPlayer is responsible for displaying
+    // the video in enterFullscreen().
+    virtual bool supportsOverlayFullscreenVideo() { return false; }
     // Instruct WebMediaPlayer to enter/exit fullscreen.
     virtual void enterFullscreen() { }