Support sample rates up to 384 kHz.

third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp

 /*
  * 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
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@@ skipping 88 matching lines @@
     // Arbitrarly limit the maximum length to 1 million frames (about 20 sec
     // at 48kHz).  The number of buckets is fairly arbitrary.
     DEFINE_STATIC_LOCAL(CustomCountHistogram, offlineContextLengthHistogram,
         ("WebAudio.OfflineAudioContext.Length", 1, 1000000, 50));
     // The limits are the min and max AudioBuffer sample rates currently
     // supported.  We use explicit values here instead of
     // AudioUtilities::minAudioBufferSampleRate() and
     // AudioUtilities::maxAudioBufferSampleRate().  The number of buckets is
     // fairly arbitrary.
     DEFINE_STATIC_LOCAL(CustomCountHistogram, offlineContextSampleRateHistogram,
-        ("WebAudio.OfflineAudioContext.SampleRate", 3000, 192000, 50));
+        ("WebAudio.OfflineAudioContext.SampleRate", 3000, 384000, 50));

[Mark P, 2016/09/13 19:06:39]

Widening the histogram like this is messy because all the buckets will shift. 
(The 50 buckets are spread exponentially between the min and maximum values, and
you're changing the maximum values.)  Technically this is okay -- entries are
emitted to the histogram under the same conditions as before -- but the
dashboard will display a mess because different buckets will overlap.

I suggest changing the name of the histogram.  (This means marking the old
histogram as obsolete and adding a new one with the same description.)

If data continuity is important to you, you can also keep emits to the old
histogram name and delete the old histogram after a while.  I.e., have two
overlapping histograms emitted for some time.

[Raymond Toy, 2016/09/13 20:12:28]

Yeah, I suspected it would make a mess of the existing data.  I'll add a new
histogram for this and think about whether to keep the old one around for a bit.

Thanks!

 
     offlineContextChannelCountHistogram.sample(numberOfChannels);
     offlineContextLengthHistogram.count(numberOfFrames);
     offlineContextSampleRateHistogram.count(sampleRate);
 
     audioContext->suspendIfNeeded();
     return audioContext;
 }
 
 OfflineAudioContext::OfflineAudioContext(Document* document, unsigned numberOfChannels, size_t numberOfFrames, float sampleRate, ExceptionState& exceptionState)
@@ skipping 321 matching lines @@
     // Note that the GraphLock is required before this check. Since this needs
     // to run on the audio thread, OfflineGraphAutoLocker must be used.
     if (m_scheduledSuspends.contains(currentSampleFrame()))
         return true;
 
     return false;
 }
 
 } // namespace blink