Support for AudioContextOptions latencyHint.

third_party/WebKit/Source/platform/audio/AudioDestination.h

Index: third_party/WebKit/Source/platform/audio/AudioDestination.h
diff --git a/third_party/WebKit/Source/platform/audio/AudioDestination.h b/third_party/WebKit/Source/platform/audio/AudioDestination.h
index dda3527f57476e3697025958418f64c07573959d..f2fe616b8be5ea76fde765340a9b0f7cefb7d835 100644
--- a/third_party/WebKit/Source/platform/audio/AudioDestination.h
+++ b/third_party/WebKit/Source/platform/audio/AudioDestination.h
@@ -45,6 +45,7 @@ namespace blink {
 class AudioFIFO;
 class AudioPullFIFO;
 class SecurityOrigin;
+class WebAudioLatencyHint;
 
 // An AudioDestination using Chromium's audio system
 
@@ -58,7 +59,7 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback,
                    const String& inputDeviceId,
                    unsigned numberOfInputChannels,
                    unsigned numberOfOutputChannels,
-                   float sampleRate,
+                   const WebAudioLatencyHint&,
                    PassRefPtr<SecurityOrigin>);
   ~AudioDestination() override;
 
@@ -70,15 +71,13 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback,
       const String& inputDeviceId,
       unsigned numberOfInputChannels,
       unsigned numberOfOutputChannels,
-      float sampleRate,
+      const WebAudioLatencyHint&,
       PassRefPtr<SecurityOrigin>);
 
   virtual void start();
   virtual void stop();
   bool isPlaying() { return m_isPlaying; }
 
-  float sampleRate() const { return m_sampleRate; }
-
   // WebAudioDevice::RenderCallback
   void render(const WebVector<float*>& sourceData,
               const WebVector<float*>& audioData,
@@ -102,7 +101,6 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback,
   unsigned m_numberOfOutputChannels;
   RefPtr<AudioBus> m_inputBus;
   RefPtr<AudioBus> m_renderBus;
-  float m_sampleRate;

[hongchan, 2016/11/15 23:46:01]

How do I query the sample rate of the destination then? This is the WebAudio
abstraction of the underlying device/thread, we don't want to lose the critical
info like the sample rate.

I am not sure if WebAudioLatencyHint can completely replace the m_sampleRate
variable.

[Andrew MacPherson, 2016/11/16 10:58:30]

My understanding is that this should be queried using
m_audioDevice->sampleRate().

   bool m_isPlaying;
   std::unique_ptr<WebAudioDevice> m_audioDevice;
   size_t m_callbackBufferSize;