Restore the HTMLVideoElement-specific prefixed fullscreen API behind a flag

Source/core/frame/UseCounter.h

 /*
  * 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 176 matching lines @@
         DOMCharacterDataModifiedEvent = 148,
         DocumentAllLegacyCall = 150,
         HTMLAppletElementLegacyCall = 151,
         HTMLEmbedElementLegacyCall = 152,
         HTMLObjectElementLegacyCall = 153,
         GetMatchedCSSRules = 155,
         SVGFontInCSS = 156,
         AttributeSpecified = 162, // Removed in DOM4.
         PrefixedAudioDecodedByteCount = 164,
         PrefixedVideoDecodedByteCount = 165,
+        PrefixedVideoSupportsFullscreen = 166,
+        PrefixedVideoDisplayingFullscreen = 167,
+        PrefixedVideoEnterFullscreen = 168,
+        PrefixedVideoExitFullscreen = 169,
+        PrefixedVideoEnterFullScreen = 170,
+        PrefixedVideoExitFullScreen = 171,
         PrefixedVideoDecodedFrameCount = 172,
         PrefixedVideoDroppedFrameCount = 173,
         PrefixedElementRequestFullscreen = 176,
         PrefixedElementRequestFullScreen = 177,
         BarPropLocationbar = 178,
         BarPropMenubar = 179,
         BarPropPersonalbar = 180,
         BarPropScrollbars = 181,
         BarPropStatusbar = 182,
         BarPropToolbar = 183,
@@ skipping 178 matching lines @@
 
     void updateMeasurements();
 
     OwnPtr<BitVector> m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace WebCore
 
 #endif // UseCounter_h