Blink changes to record interest rects for http://w3c.github.io/frame-timing/

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 689 matching lines @@
         FullscreenInsecureOrigin = 766,
         DialogInSandboxedContext = 767,
         SVGSMILAnimationInImageRegardlessOfCache = 768,
         PushSubscriptionId = 769,
         EncryptedMediaSecureOrigin = 770,
         EncryptedMediaInsecureOrigin = 771,
         MarkDequeOverflow = 772,
         StoreBufferOverflow = 773,
         SlotsBufferOverflow = 774,
         ObjectObserve = 775,
+        UnprefixedPerformanceClearFrameTimings = 776,

[chrishtr, 2015/05/09 00:51:52]

Why have Unprefixed at the start?

[MikeB, 2015/05/11 23:10:51]

Because I saw 
        UnprefixedPerformanceTimeline = 65,
        UnprefixedUserTiming = 67,
etc.
Happy to not have the 'Unprefixed' part if it's unnecessary.
I can just consolidate it as PerformanceFrameTiming and not have a separate one
for clear* and set*buffersize too.

[chrishtr, 2015/05/11 23:46:43]

Looks like this is because PrefixedPerformanceTimeline used to be enum value 66
(try a code search to see remnants).
You can just remove Unprefixed, since this complication doesn't apply to you.

I agree that combining them into a single UseCounter for PerformanceFrameTiming
is better, since we just want to count the usage of the overall feature.

+        UnprefixedPerformanceSetFrameTimingBufferSize = 777,
 
         // 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 83 matching lines @@
 
     bool hasRecordedMeasurement(Feature feature) const { return m_countBits.hasRecordedMeasurement(feature); }
 
     CountBits m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace blink
 
 #endif // UseCounter_h