Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/media/renderer_webmediaplayer_delegate.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/renderer_webmediaplayer_delegate.h"
 
 #include <stdint.h>
 
 #include "base/auto_reset.h"
 #include "content/common/media/media_player_delegate_messages.h"
@@ skipping 156 matching lines @@
       it = idle_delegate_map_.erase(it);
     else
       ++it;
   }
 
   // Shutdown the timer if no delegates are left.
   if (idle_delegate_map_.empty())
     idle_cleanup_timer_.Stop();
 }
 
+void RendererWebMediaPlayerDelegate::OnDestruct() {
+  delete this;
+}
+
 }  // namespace media