Remove useless override of executionContext() in HTMLMediaElement

Remove useless override of executionContext() in HTMLMediaElement. This was
previously done to remove ambiguity because HTMLMediaElement inherited two
implementations of executionContext() from its base classes (Node and
ActiveDOMObject). This CL gets rid of the override and uses a "using"
statement instead to remove ambiguity, which is the proper way to do this.

The executionContext() override in Node can now be marked as FINAL as a
result.

R=tkent@chromium.org

Review URL: https://codereview.chromium.org/334063002

git-svn-id: svn://svn.chromium.org/blink/trunk@176167 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/dom/Node.h

@@ -613,7 +613,7 @@ public:
     virtual Node* toNode() OVERRIDE FINAL;
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
-    virtual ExecutionContext* executionContext() const OVERRIDE;
+    virtual ExecutionContext* executionContext() const OVERRIDE FINAL;
 
     virtual bool addEventListener(const AtomicString& eventType, PassRefPtr<EventListener>, bool useCapture = false) OVERRIDE;
     virtual bool removeEventListener(const AtomicString& eventType, EventListener*, bool useCapture = false) OVERRIDE;

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

@@ -235,7 +235,7 @@ public:
     // causes an ambiguity error at compile time. This class's constructor
     // ensures that both implementations return document, so return the result
     // of one of them here.
-    virtual ExecutionContext* executionContext() const OVERRIDE FINAL { return HTMLElement::executionContext(); }
+    using HTMLElement::executionContext;
 
     bool hasSingleSecurityOrigin() const { return !m_player || m_player->hasSingleSecurityOrigin(); }