Let the WebMediaPlayer decide whether to use overlay video.

public/platform/WebMediaPlayer.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 158 matching lines @@
     // Returns whether keySystem is supported. If true, the result will be
     // reported by an event.
     virtual MediaKeyException generateKeyRequest(const WebString& keySystem, const unsigned char* initData, unsigned initDataLength) { return MediaKeyExceptionKeySystemNotSupported; }
     virtual MediaKeyException addKey(const WebString& keySystem, const unsigned char* key, unsigned keyLength, const unsigned char* initData, unsigned initDataLength, const WebString& sessionId) { return MediaKeyExceptionKeySystemNotSupported; }
     virtual MediaKeyException cancelKeyRequest(const WebString& keySystem, const WebString& sessionId) { return MediaKeyExceptionKeySystemNotSupported; }
     virtual void setContentDecryptionModule(WebContentDecryptionModule* cdm, WebContentDecryptionModuleResult result) { result.completeWithError(WebContentDecryptionModuleExceptionNotSupportedError, 0, "ERROR"); }
 
     // 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() { }
 
     virtual void enabledAudioTracksChanged(const WebVector<TrackId>& enabledTrackIds) { }
     // |selectedTrackId| is null if no track is selected.
     virtual void selectedVideoTrackChanged(TrackId* selectedTrackId) { }
 };
 
 } // namespace blink
 
 #endif