Add a deprecation warning for document.clear()

Source/core/page/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 112 matching lines @@
         SVGTRefElement,
         UnprefixedPerformanceTimeline,
         PrefixedPerformanceTimeline,
         UnprefixedUserTiming,
         PrefixedUserTiming,
         WindowEvent,
         ContentSecurityPolicyWithBaseElement,
         PrefixedMediaAddKey,
         PrefixedMediaGenerateKeyRequest,
         WebAudioLooping,
+        DocumentClear,
         // Add new features above this line. Don't change assigned numbers of each items.
         NumberOfFeatures, // This enum value must be last.
     };
 
     // "count" sets the bit for this feature to 1. Repeated calls are ignored.
     static void count(Document*, Feature);
     static void count(DOMWindow*, Feature);
 
     // "countDeprecation" sets the bit for this feature to 1, and sends a deprecation
     // warning to the console. Repeated calls are ignored.
@@ skipping 25 matching lines @@
     }
 
     void updateMeasurements();
 
     OwnPtr<BitVector> m_countBits;
 };
 
 } // namespace WebCore
 
 #endif // UseCounter_h