Bug 833283 - Add do_QueryFrame support to nsVideoFrame. r=bz

Ms2ger recommended this instead of using do_QueryInterface on
nsVideoFrame.

layout/generic/nsVideoFrame.cpp

@@ -58,6 +58,7 @@ nsVideoFrame::~nsVideoFrame()
 }
 
 NS_QUERYFRAME_HEAD(nsVideoFrame)
+  NS_QUERYFRAME_ENTRY(nsVideoFrame)
   NS_QUERYFRAME_ENTRY(nsIAnonymousContentCreator)
 NS_QUERYFRAME_TAIL_INHERITING(nsContainerFrame)
 

layout/generic/nsVideoFrame.h

@@ -41,6 +41,7 @@ public:
   nsVideoFrame(nsStyleContext* aContext);
 
   NS_DECL_QUERYFRAME
+  NS_DECL_QUERYFRAME_TARGET(nsVideoFrame)
   NS_DECL_FRAMEARENA_HELPERS
 
   virtual void BuildDisplayList(nsDisplayListBuilder*   aBuilder,