Let Contraints Controll Mute/Unmute Audio Local Playback For Desktop Sharing

content/renderer/media/user_media_client_impl.cc

 // 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.
 
 #include "content/renderer/media/user_media_client_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 #include <vector>
@@ skipping 67 matching lines @@
     if (audio_basic.hotwordEnabled.hasExact()) {
       controls->hotword_enabled = audio_basic.hotwordEnabled.exact();
     } else {
       for (const auto& audio_advanced : request.audioConstraints().advanced()) {
         if (audio_advanced.hotwordEnabled.hasExact()) {
           controls->hotword_enabled = audio_advanced.hotwordEnabled.exact();
           break;
         }
       }
     }
+
+    bool exact = request.audioConstraints().basic().disableLocalEcho.exact();

[Sergey Ulanov, 2016/10/12 22:21:01]

this doesn't look like a good variable name. Also it looks wrong to call exact()
if hasExcat() returns false. Why can't this code follow the same pattern that's
used above for hotword_enabled:
  if (request.audioConstraints().basic().disableLocalEcho.hasExact()) {
    controls->disable_local_echo =
         request.audioConstraints().basic().disableLocalEcho.exact();
  } else {
    controls->disable_local_echo =
        controls->audio.stream_source != kMediaStreamSourceDesktop;
  }

Or even this:
  controls->disable_local_echo =
     request.audioConstraints().basic().disableLocalEcho.hasExact()
        ? request.audioConstraints().basic().disableLocalEcho.exact()
        : controls->audio.stream_source != kMediaStreamSourceDesktop;

[qiangchen, 2016/10/12 22:49:54]

Done.

+    bool has_exact =
+        request.audioConstraints().basic().disableLocalEcho.hasExact();
+
+    if (has_exact) {
+      controls->disable_local_echo = exact;
+    } else {
+      controls->disable_local_echo =
+          controls->audio.stream_source != kMediaStreamSourceDesktop;
+    }
   }
   if (!request.videoConstraints().isNull()) {
     const blink::WebMediaTrackConstraintSet& video_basic =
         request.videoConstraints().basic();
     CopyFirstString(video_basic.mediaStreamSource.exact(),
                     &(controls->video.stream_source));
     CopyVector(video_basic.deviceId.exact(), &(controls->video.device_ids));
     CopyVector(video_basic.deviceId.ideal(),
                &(controls->video.alternate_device_ids));
     for (const auto& constraint : request.videoConstraints().advanced()) {
@@ skipping 1088 matching lines @@
 
 bool UserMediaClientImpl::UserMediaRequestInfo::HasPendingSources() const {
   return !sources_waiting_for_callback_.empty();
 }
 
 void UserMediaClientImpl::OnDestruct() {
   delete this;
 }
 
 }  // namespace content