Support AudioContextOptions latencyHint as double.

content/renderer/media/audio_renderer_mixer_manager.h

Index: content/renderer/media/audio_renderer_mixer_manager.h
diff --git a/content/renderer/media/audio_renderer_mixer_manager.h b/content/renderer/media/audio_renderer_mixer_manager.h
index 7d77212bbe64eed8938ace0f930891ddc827908a..d50cb969fbca9423339af523e45e50db532609dc 100644
--- a/content/renderer/media/audio_renderer_mixer_manager.h
+++ b/content/renderer/media/audio_renderer_mixer_manager.h
@@ -116,13 +116,13 @@ class CONTENT_EXPORT AudioRendererMixerManager
       if (a.params.channels() != b.params.channels())
         return a.params.channels() < b.params.channels();
 
-      if (a.latency != b.latency)
+      if ((a.latency == media::AudioLatency::LATENCY_EXACT_MS ||
+           b.latency == media::AudioLatency::LATENCY_EXACT_MS) &&
+          a.params.GetBufferDuration() != b.params.GetBufferDuration()) {
+        return a.params.GetBufferDuration() < b.params.GetBufferDuration();
+      } else if (a.latency != b.latency)

[Andrew MacPherson, 2017/03/14 12:03:03]

In audio_renderer_mixer_manager_unittest.cc it's expected that changing the
'latency' value will use a new mixer, even if the underlying buffer size is the
same. Should this still be the case, or should this just be a check for
GetBufferDuration() in all cases now without looking at the specific 'latency'
value?

[o1ka, 2017/03/14 15:55:43]

Let's not touch mixers at all. WebAudio is not supposed to go through them as of
now - the experiment for that is closed. If later it's re-opened, we'll hit a
DCHECK and fix the code.

[Andrew MacPherson, 2017/03/15 15:08:17]

Ok great, I've reverted this now.

         return a.latency < b.latency;
 
-      // TODO(olka) add buffer duration comparison for LATENCY_EXACT_MS when
-      // adding support for it.
-      DCHECK_NE(media::AudioLatency::LATENCY_EXACT_MS, a.latency);
-
       // Ignore effects(), bits_per_sample(), format(), and frames_per_buffer(),
       // these parameters do not affect mixer reuse.  All AudioRendererMixer
       // units disable FIFO, so frames_per_buffer() can be safely ignored.