Add usage counter for each value of webkit-user-modify

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 1430 matching lines @@
     V8MediaSession_Metadata_AttributeGetter = 1788,
     V8MediaSession_Metadata_AttributeSetter = 1789,
     V8MediaSession_PlaybackState_AttributeGetter = 1790,
     V8MediaSession_PlaybackState_AttributeSetter = 1791,
     V8MediaSession_SetActionHandler_Method = 1792,
     WebNFCPush = 1793,
     WebNFCCancelPush = 1794,
     WebNFCWatch = 1795,
     WebNFCCancelWatch = 1796,
     AudioParamCancelAndHoldAtTime = 1797,
+    CSSValueUserModifyReadOnly = 1798,

[Manuel Rego, 2017/02/03 14:12:07]

Not really important but we usually have comments like:
  // The above items are available in M56 branch.

As M57 branch has just happened, maybe it'd be nice to add this.

This makes easier to follow in which releases the use counters
have been introduced.

[Xiaocheng, 2017/02/03 14:35:13]

Thanks, with a question.

Counters starting from 1788 are added in M58, and some of them are merged to M57
(1788-1792 are merged, 1797 is merge-approved).

In this case, where should the comment be put at?

[Manuel Rego, 2017/02/03 14:46:22]

That's a good question and I don't have a good answer for it.

What I think is that it's valuable to have those comments,
maybe we should put it before 1793; and move 1797 just after 1792.
But it can be confusing too.

Dunno if @haraken has the right answer.

+    CSSValueUserModifyReadWrite = 1799,
+    CSSValueUserModifyReadWritePlaintextOnly = 1800,
 
     // 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 68 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