Clarify that a document().frame() access in HTMLMediaElement cannot be null

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1032 matching lines @@
     m_webMediaPlayer->setVolume(effectiveMediaVolume());
 
     m_webMediaPlayer->setPoster(posterImageURL());
 
     m_webMediaPlayer->setPreload(effectivePreloadType());
 
     m_webMediaPlayer->load(loadType(), kurl, corsMode());
 
     if (isFullscreen()) {
         // This handles any transition to or from fullscreen overlay mode.
-        document().frame()->chromeClient().enterFullScreenForElement(this);
+        frame->chromeClient().enterFullScreenForElement(this);
     }
 }
 
 void HTMLMediaElement::setPlayerPreload()
 {
     if (m_webMediaPlayer)
         m_webMediaPlayer->setPreload(effectivePreloadType());
 
     if (loadIsDeferred() && preloadType() != WebMediaPlayer::PreloadNone)
         startDeferredLoad();
@@ skipping 2581 matching lines @@
     visitor->trace(m_client);
 }
 
 DEFINE_TRACE(HTMLMediaElement::AudioSourceProviderImpl)
 {
     visitor->trace(m_client);
 }
 #endif
 
 }