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..5c62b4fd0ae6368fb4d0f662d2351dc3cb3f94b9 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;
 
@@ -70,14 +71,20 @@ 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; }
+  double sampleRate() const {
+    return m_audioDevice ? m_audioDevice->sampleRate() : 0;

[o1ka, 2016/11/30 11:46:27]

Here and below: if |m_audioDevice| being nullptr is not a normal situation, we
should not mask it here by checking for nullptr; it's better to crash
immediately.

[Raymond Toy, 2016/11/30 21:50:27]

I agree with this. Plus there's already an ASSERT in AudioDestination.cpp that
m_audioDevice is not null.

Having said that, the general style in WebAudio is to check for bad things and
if they're bad, silently return.  I don't know why that is, because I prefer bad
things to crash the renderer instead of silently proceeding to produce silence
in weird ways.

[Andrew MacPherson, 2016/12/01 12:11:56]

Done.

+  }
+
+  int framesPerBuffer() const {
+    return m_audioDevice ? m_audioDevice->framesPerBuffer() : 0;
+  }
 
   // WebAudioDevice::RenderCallback
   void render(const WebVector<float*>& sourceData,
@@ -102,7 +109,6 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback,
   unsigned m_numberOfOutputChannels;
   RefPtr<AudioBus> m_inputBus;
   RefPtr<AudioBus> m_renderBus;
-  float m_sampleRate;
   bool m_isPlaying;
   std::unique_ptr<WebAudioDevice> m_audioDevice;
   size_t m_callbackBufferSize;