Make WebMediaPlayer::didLoadingProgress() non-const.

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 111 matching lines @@
     // Getters of playback state.
     virtual bool paused() const = 0;
     virtual bool seeking() const = 0;
     virtual double duration() const = 0;
     virtual double currentTime() const = 0;
 
     // Internal states of loading and network.
     virtual NetworkState networkState() const = 0;
     virtual ReadyState readyState() const = 0;
 
-    virtual bool didLoadingProgress() const = 0;
+    virtual bool didLoadingProgress() = 0;
 
     virtual bool hasSingleSecurityOrigin() const = 0;
     virtual bool didPassCORSAccessCheck() const = 0;
 
     virtual double mediaTimeForTimeValue(double timeValue) const = 0;
 
     virtual unsigned decodedFrameCount() const = 0;
     virtual unsigned droppedFrameCount() const = 0;
     virtual unsigned corruptedFrameCount() const { return 0; };
     virtual unsigned audioDecodedByteCount() const = 0;
@@ skipping 17 matching lines @@
     // Instruct WebMediaPlayer to enter/exit fullscreen.
     virtual void enterFullscreen() { }
     virtual void exitFullscreen() { }
     // Returns true if the player can enter fullscreen.
     virtual bool canEnterFullscreen() const { return false; }
 };
 
 } // namespace blink
 
 #endif