Add UMA histograms for WebAudio

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

Index: third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
index dc3afb966c3be24c02b0a5c034ddb0727f8a75d7..1bf36e7fd458713ce98bf49595ea948953ace9e1 100644
--- a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
@@ -35,6 +35,7 @@
 #include "modules/webaudio/OfflineAudioCompletionEvent.h"
 #include "modules/webaudio/OfflineAudioDestinationNode.h"
 
+#include "platform/Histogram.h"
 #include "platform/audio/AudioUtilities.h"
 
 namespace blink {
@@ -90,6 +91,24 @@ OfflineAudioContext* OfflineAudioContext::create(ExecutionContext* context, unsi
             + ")");
     }
 
+    DEFINE_STATIC_LOCAL(SparseHistogram, offlineContextChannelCountHistogram,
+        ("WebAudio.OfflineAudioContext.ChannelCount"));
+    // 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, 19200, 50));
+
+    offlineContextChannelCountHistogram.sample(numberOfChannels);
+    offlineContextLengthHistogram.count(numberOfFrames);
+    offlineContextSampleRateHistogram.count(sampleRate);
+
     audioContext->suspendIfNeeded();
     return audioContext;
 }