Support AudioContextOptions latencyHint as double.

content/renderer/media/audio_renderer_mixer_manager.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
 #define CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
 
 #include <bitset>
 #include <map>
 #include <memory>
@@ skipping 98 matching lines @@
 
   // Custom compare operator for the AudioRendererMixerMap.  Allows reuse of
   // mixers where only irrelevant keys mismatch; e.g., effects, bits per sample.
   struct MixerKeyCompare {
     bool operator()(const MixerKey& a, const MixerKey& b) const {
       if (a.source_render_frame_id != b.source_render_frame_id)
         return a.source_render_frame_id < b.source_render_frame_id;
       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.
       if (a.params.channel_layout() != b.params.channel_layout())
         return a.params.channel_layout() < b.params.channel_layout();
 
       if (media::AudioDeviceDescription::IsDefaultDevice(a.device_id) &&
           media::AudioDeviceDescription::IsDefaultDevice(b.device_id)) {
         // Both device IDs represent the same default device => do not compare
         // them; the default device is always authorized => ignoring security
@@ skipping 31 matching lines @@
   // Map of the output latencies encountered throughout mixer manager lifetime.
   // Used for UMA histogram logging.
   std::bitset<media::AudioLatency::LATENCY_COUNT> latency_map_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_