Add UseCounter for <applet> (a boy can dream, can't he?)

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 280 matching lines @@
         PromiseConstructor = 270,
         PromiseCast = 271,
         PromiseReject = 272,
         PromiseResolve = 273,
         TextAutosizing = 274,
         TextAutosizingLayout = 275,
         HTMLAnchorElementPingAttribute = 276,
         JavascriptExhaustedMemory = 277,
         InsertAdjacentHTML = 278,
         SVGClassName = 279,
+        HTMLAppletElement = 280,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         NumberOfFeatures, // This enum value must be last.
     };
 
     // "count" sets the bit for this feature to 1. Repeated calls are ignored.
     static void count(const Document&, Feature);
     static void count(const ExecutionContext*, Feature);
     void count(CSSParserContext, CSSPropertyID);
     void count(Feature);
@@ skipping 35 matching lines @@
 
     void updateMeasurements();
 
     OwnPtr<BitVector> m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace WebCore
 
 #endif // UseCounter_h