Add three UseCounters for LABEL element.

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 1068 matching lines @@
         V8Animation_Id_AttributeGetter = 1239,
         V8Animation_Id_AttributeSetter = 1240,
         MediaStreamOnEnded = 1241,
         DocumentCreateEventInputEvent = 1242,
         WebAnimationHyphenatedProperty = 1243,
         FormControlsCollectionReturnsRadioNodeListForFieldSet = 1244,
         ApplicationCacheManifestSelectInsecureOrigin = 1245,
         ApplicationCacheManifestSelectSecureOrigin = 1246,
         ApplicationCacheAPIInsecureOrigin = 1247,
         ApplicationCacheAPISecureOrigin = 1248,
+        // The above items are available in M50 branch
+
+        HTMLLabelElementFormIsDifferentFromControlForm = 1261,
+        HTMLLabelElementHasNoControlAndFormIsAncestor = 1262,
+        HTMLLabelElementControlForNonFormAssociatedElement = 1263,
 
         // 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 Frame*, Feature);
@@ skipping 74 matching lines @@
     friend class UseCounterTest;
     static int m_muteCount;
 
     CountBits m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace blink
 
 #endif // UseCounter_h