Adding UseCounter specific for extensions

third_party/WebKit/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 1583 matching lines @@
   bool hasRecordedMeasurement(Feature) const;
 
   DECLARE_TRACE();
 
  private:
   // Notifies that a feature is newly counted to |m_observers|. This shouldn't
   // be called when the counter is disabled by |m_muteCount| or
   // |m_disableReporting|.
   void notifyFeatureCounted(Feature);
 
+  EnumerationHistogram& extensionFeaturesHistogram() const;
   EnumerationHistogram& featuresHistogram() const;
   EnumerationHistogram& cssHistogram() const;
   EnumerationHistogram& animatedCSSHistogram() const;
 
   // If non-zero, ignore all 'count' calls completely.
   unsigned m_muteCount;
 
   // If true, disable reporting all histogram entries.
   bool m_disableReporting;
 
@@ skipping 23 matching lines @@
     // Tracks what features/properties need to be reported to the legacy
     // histograms.
     BitVector m_featureBits;
     BitVector m_CSSBits;
   } m_legacyCounter;
 };
 
 }  // namespace blink
 
 #endif  // UseCounter_h