Let toParentMediaElement return null for the media element itself

Source/core/html/shadow/MediaControlElementTypes.cpp

 /*
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 33 matching lines @@
 using namespace HTMLNames;
 
 class Event;
 
 HTMLMediaElement* toParentMediaElement(Node* node)
 {
     if (!node)
         return 0;
     Node* mediaNode = node->shadowHost();
     if (!mediaNode)
-        mediaNode = node;
+        return 0;

[fs, 2014/09/24 15:48:16]

paintMediaSliderThumb and paintMediaVolumeSliderThumb both seem to pass
renderer->node()->shadowHost() as node - which seems strange to me. It seems
that could/would trigger this code-path as well?

[philipj_slow, 2014/09/25 07:53:10]

They pass renderer->node()->shadowHost() because the sliders are themselves
implemented using shadow DOM. It all seems to work at least, and if one uses
toParentMediaElement(object->node()->shadowHost()) e.g. in
paintMediaPlayButton() that button fails to be painted.

[fs, 2014/09/25 09:30:19]

Ok, I figured it'd be something like that. LGTM.

     if (!isHTMLMediaElement(mediaNode))
         return 0;
 
     return toHTMLMediaElement(mediaNode);
 }
 
 MediaControlElementType mediaControlElementType(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(node->isMediaControlElement());
     HTMLElement* element = toHTMLElement(node);
@@ skipping 79 matching lines @@
     , m_currentValue(0)
 {
 }
 
 void MediaControlTimeDisplayElement::setCurrentValue(double time)
 {
     m_currentValue = time;
 }
 
 } // namespace blink