Setting HTMLMediaElement.controller does not properly remove the 'mediagroup' content attribute

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index 6f0f83019dfb79df2273087aa2aa934d7284622c..e5f0ce60badccc8e35eb045f0ef498ce29bdb197 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -276,11 +276,8 @@ public:
     enum InvalidURLAction { DoNothing, Complain };
     bool isSafeToLoadURL(const KURL&, InvalidURLAction);
 
-    const String& mediaGroup() const;
-    void setMediaGroup(const String&);
-
     MediaController* controller() const;
-    void setController(PassRefPtr<MediaController>);
+    void setController(PassRefPtr<MediaController>); // Resets the MediaGroup and sets the MediaController.
 
 protected:
     HTMLMediaElement(const QualifiedName&, Document&, bool);
@@ -299,6 +296,8 @@ protected:
 
     virtual bool isMediaElement() const OVERRIDE { return true; }
 
+    void setControllerInternal(PassRefPtr<MediaController>);
+
     // Restrictions to change default behaviors.
     enum BehaviorRestrictionFlags {
         NoRestrictions = 0,
@@ -452,6 +451,8 @@ private:
 
     void removeBehaviorsRestrictionsAfterFirstUserGesture();
 
+    const AtomicString& mediaGroup() const;
+    void setMediaGroup(const AtomicString&);
     void updateMediaController();
     bool isBlocked() const;
     bool isBlockedOnMediaController() const;
@@ -559,7 +560,6 @@ private:
     MediaElementAudioSourceNode* m_audioSourceNode;
 #endif
 
-    String m_mediaGroup;
     friend class MediaController;
     RefPtr<MediaController> m_mediaController;