Add UMA histograms for WebAudio

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

Index: third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.cpp
index fcfa28d9c3f55cbcff6d24dc9f2ce5767d40f202..f91950fd27c14fe4bc555b0a2cb5f8766674064f 100644
--- a/third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AbstractAudioContext.cpp
@@ -64,6 +64,7 @@
 #include "modules/webaudio/ScriptProcessorNode.h"
 #include "modules/webaudio/StereoPannerNode.h"
 #include "modules/webaudio/WaveShaperNode.h"
+#include "platform/Histogram.h"
 #include "platform/ThreadSafeFunctional.h"
 #include "platform/audio/IIRFilter.h"
 #include "public/platform/Platform.h"
@@ -206,7 +207,34 @@ AudioBuffer* AbstractAudioContext::createBuffer(unsigned numberOfChannels, size_
     // It's ok to call createBuffer, even if the context is closed because the AudioBuffer doesn't
     // really "belong" to any particular context.
 
-    return AudioBuffer::create(numberOfChannels, numberOfFrames, sampleRate, exceptionState);
+    AudioBuffer* buffer = AudioBuffer::create(numberOfChannels, numberOfFrames, sampleRate, exceptionState);
+
+    if (buffer) {
+        // Only record the data if the creation succeeded.
+        DEFINE_STATIC_LOCAL(SparseHistogram, audioBufferChannelsHistogram,
+            ("WebAudio.AudioBuffer.NumberOfChannels"));
+        DEFINE_STATIC_LOCAL(SparseHistogram, audioBufferLengthHistogram,
+            ("WebAudio.AudioBuffer.Length"));
+        DEFINE_STATIC_LOCAL(SparseHistogram, audioBufferSampleRateHistogram,

[hongchan, 2016/05/18 22:07:01]

I think we can move anything related to the sample rate to the inside of if()
clause below.

[Raymond Toy, 2016/05/18 22:25:30]

The sample rate for the buffer is an argument to createBuffer.  So you only want
to record the sample rate only for contexts that aren't closed?  I think we
would get more (indirect) information if we always record the sample rate but
only record the ratio when the context is not closed.  Then the difference
between the number of samples taken between the two tells us how often people
create buffers on closed contexts. 

But sample rate ratio histogram can, of course, go inside the if block below.

[hongchan, 2016/05/19 21:43:53]

Acknowledged.

+            ("WebAudio.AudioBuffer.SampleRate"));
+        DEFINE_STATIC_LOCAL(SparseHistogram, audioBufferSampleRateRatioHistogram,

[hongchan, 2016/05/19 21:43:53]

Yes, I think this needs to be inside of the if clause below.

[Raymond Toy, 2016/05/20 20:21:25]

Done.

+            ("WebAudio.AudioBuffer.SampleRateRatio"));
+        audioBufferChannelsHistogram.sample(numberOfChannels);
+        audioBufferLengthHistogram.sample(clampTo(numberOfFrames, 0, std::numeric_limits<int>::max()));
+        audioBufferSampleRateHistogram.sample(static_cast<int>(sampleRate));
+
+        // Compute the ratio of the buffer rate and the context rate so we know
+        // how often the buffer needs to be resampled to match the context.  For
+        // the histogram, we multiply the ratio by 100 and round to the nearest
+        // integer.  If the context is closed, don't record this because we
+        // don't have a sample rate for closed context.
+        if (!isContextClosed()) {
+            float ratio = 100 * sampleRate / this->sampleRate();
+            audioBufferSampleRateRatioHistogram.sample(static_cast<int>(ratio + 0.5));
+        }
+    }
+
+    return buffer;
 }
 
 ScriptPromise AbstractAudioContext::decodeAudioData(ScriptState* scriptState, DOMArrayBuffer* audioData, AudioBufferCallback* successCallback, AudioBufferCallback* errorCallback, ExceptionState& exceptionState)