Measure current usage statistics for MediaStream label and stop() before going for deprecation.

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 484 matching lines @@
         MediaStreamEnded = 526,
         MixedContentPrivateIPInPublicWebsitePassive = 527,
         MixedContentPrivateIPInPublicWebsiteActive = 528,
         XMLExternalResourceLoad = 529,
         MixedContentPrivateHostnameInPublicHostname = 530,
         LegacyProtocolEmbeddedAsSubresource = 531,
         RequestedSubresourceWithEmbeddedCredentials = 532,
         NotificationCreated = 533,
         NotificationClosed = 534,
         NotificationPermissionRequested = 535,
+        MediaStreamLabel = 536,
+        MediaStreamStop = 537,
 
         // 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.
     };
 
     // "count" sets the bit for this feature to 1. Repeated calls are ignored.
     static void count(const Document&, Feature);
@@ skipping 51 matching lines @@
 
     void updateMeasurements();
 
     OwnPtr<BitVector> m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace blink
 
 #endif // UseCounter_h