Mixing audio with different latency requirements

media/base/audio_renderer_mixer.cc

Index: media/base/audio_renderer_mixer.cc
diff --git a/media/base/audio_renderer_mixer.cc b/media/base/audio_renderer_mixer.cc
index 008fcce793320af352ff80ab17ff51c8ea17cff3..83539692048f1c7faafdcd596860e5a393489b14 100644
--- a/media/base/audio_renderer_mixer.cc
+++ b/media/base/audio_renderer_mixer.cc
@@ -10,20 +10,52 @@
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 
 namespace media {
 
 enum { kPauseDelaySeconds = 10 };
 
+// Tracks the maximum value of a counter and logs it into a UMA histogram upon
+// the destruciton.
+class AudioRendererMixer::UMAMaxValueTracker {
+ public:
+  UMAMaxValueTracker(const std::string& histogram_name)
+      : histogram_name_(histogram_name), count_(0), max_count_(0) {}
+
+  ~UMAMaxValueTracker() {
+    if (max_count_ && !histogram_name_.empty())
+      LOCAL_HISTOGRAM_CUSTOM_COUNTS(histogram_name_, max_count_, 1, 100, 100);
+  }
+
+  // Increments the counter, updates the maximum.
+  void Increment() {
+    ++count_;
+    if (max_count_ < count_)
+      max_count_ = count_;
+  }
+
+  // Decrements the counter.
+  void Decrement() { --count_; }
+
+ private:
+  const std::string histogram_name_;
+  int count_;
+  int max_count_;
+  DISALLOW_COPY_AND_ASSIGN(UMAMaxValueTracker);
+};
+
 AudioRendererMixer::AudioRendererMixer(const AudioParameters& output_params,
-                                       scoped_refptr<AudioRendererSink> sink)
+                                       scoped_refptr<AudioRendererSink> sink,
+                                       const std::string& histogram_name)
     : output_params_(output_params),
       audio_sink_(std::move(sink)),
       master_converter_(output_params, output_params, true),
       pause_delay_(base::TimeDelta::FromSeconds(kPauseDelaySeconds)),
       last_play_time_(base::TimeTicks::Now()),
       // Initialize |playing_| to true since Start() results in an auto-play.
-      playing_(true) {
+      playing_(true),
+      input_count_tracker_(new UMAMaxValueTracker(histogram_name)) {
   DCHECK(audio_sink_);
   audio_sink_->Initialize(output_params, this);
   audio_sink_->Start();
@@ -70,6 +102,8 @@ void AudioRendererMixer::AddMixerInput(const AudioParameters& input_params,
     }
     converter->second->AddInput(input);
   }
+
+  input_count_tracker_->Increment();
 }
 
 void AudioRendererMixer::RemoveMixerInput(
@@ -91,6 +125,8 @@ void AudioRendererMixer::RemoveMixerInput(
       converters_.erase(converter);
     }
   }
+
+  input_count_tracker_->Decrement();
 }
 
 void AudioRendererMixer::AddErrorCallback(const base::Closure& error_cb) {