Add UMA histograms for WebAudio

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

Index: third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
index ecaffd59494a65c28508c31ca42b1d9fabb61eda..f7cc9c928a7f3b814c40749e345b535337eaaf75 100644
--- a/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
@@ -10,6 +10,7 @@
 #include "core/dom/DOMException.h"
 #include "core/dom/ExceptionCode.h"
 #include "modules/webaudio/AudioBufferCallback.h"
+#include "platform/Histogram.h"
 #include "platform/audio/AudioUtilities.h"
 
 #if DEBUG_AUDIONODE_REFERENCES
@@ -66,6 +67,13 @@ AbstractAudioContext* AudioContext::create(Document& document, ExceptionState& e
         audioContext, audioContext->m_contextId, s_hardwareContextCount);
 #endif
 
+    DEFINE_STATIC_LOCAL(SparseHistogram, maxChannelCountHistogram,
+        ("WebAudio.AudioContext.MaxChannelsAvailable"));
+    DEFINE_STATIC_LOCAL(SparseHistogram, sampleRateHistogram,
+        ("WebAudio.AudioContext.HardwareSampleRate"));

[Mark P, 2016/06/10 04:02:53]

Is this generally fixed or should this be a custom histogram too?

[Raymond Toy, 2016/06/10 15:13:44]

We expect the possible values for the hardware sample rate to be from a fairly
small set.  Our expectations are that 44100, 48000, 88200, 96000, and 192000
represent basically all of the possible values.  We have some suspicions that
there are some other values, though and we'd like to capture the actual value.

+    maxChannelCountHistogram.sample(audioContext->destination()->maxChannelCount());
+    sampleRateHistogram.sample(audioContext->sampleRate());
+
     return audioContext;
 }