Let toParentMediaElement return null for the media element itself

Source/core/html/shadow/MediaControlElementTypes.cpp

Index: Source/core/html/shadow/MediaControlElementTypes.cpp
diff --git a/Source/core/html/shadow/MediaControlElementTypes.cpp b/Source/core/html/shadow/MediaControlElementTypes.cpp
index 9094ed82328d9d9ce2930a26102cd73f13f729a9..78f1a2cfd8c19ea043dfa676866150ac7adcefb5 100644
--- a/Source/core/html/shadow/MediaControlElementTypes.cpp
+++ b/Source/core/html/shadow/MediaControlElementTypes.cpp
@@ -51,7 +51,7 @@ HTMLMediaElement* toParentMediaElement(Node* 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;