Add a use counter for RtcpMuxPolicy of "negotiate".

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 1452 matching lines @@
     UncancellableTouchEventPreventDefaulted = 1813,
     UncancellableTouchEventDueToMainThreadResponsivenessPreventDefaulted = 1814,
     V8HTMLVideoElement_Poster_AttributeGetter = 1815,
     V8HTMLVideoElement_Poster_AttributeSetter = 1816,
     NotificationPermissionRequestedIframe = 1817,
     FileReaderSyncInServiceWorker = 1818,
     PresentationReceiverInsecureOrigin = 1819,
     PresentationReceiverSecureOrigin = 1820,
     PresentationRequestInsecureOrigin = 1821,
     PresentationRequestSecureOrigin = 1822,
+    RtcpMuxPolicyNegotiate = 1823,
 
     // Add new features immediately above this line. Don't change assigned
     // numbers of any item, and don't reuse removed slots.
     // Also, run update_use_counter_feature_enum.py in
     // chromium/src/tools/metrics/histograms/ to update the UMA mapping.
     NumberOfFeatures,  // This enum value must be last.
   };
 
   // An interface to observe UseCounter changes. Note that this is never
   // notified when the counter is disabled by |m_muteCount| or
@@ skipping 89 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