Add a use-counter for viewport-fixed position:fixed under a filter

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 1556 matching lines @@
     kMediaStreamConstraintsGoogNoiseSuppression = 1951,
     kMediaStreamConstraintsGoogHighpassFilter = 1952,
     kMediaStreamConstraintsGoogTypingNoiseDetection = 1953,
     kMediaStreamConstraintsGoogExperimentalNoiseSuppression = 1954,
     kMediaStreamConstraintsGoogBeamforming = 1955,
     kMediaStreamConstraintsGoogArrayGeometry = 1956,
     kMediaStreamConstraintsGoogAudioMirroring = 1957,
     kMediaStreamConstraintsGoogDAEchoCancellation = 1958,
     kMediaStreamConstraintsGoogNoiseReduction = 1959,
     kMediaStreamConstraintsGoogPowerLineFrequency = 1960,
+    kViewportFixedPositionUnderFilter = 1961,
 
     // 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.
     kNumberOfFeatures,  // 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 99 matching lines @@
     // Tracks what features/properties need to be reported to the legacy
     // histograms.
     BitVector feature_bits_;
     BitVector css_bits_;
   } legacy_counter_;
 };
 
 }  // namespace blink
 
 #endif  // UseCounter_h