Unmute Tab Audio For Desktop Share By Default

content/browser/renderer_host/media/audio_input_renderer_host.cc

Index: content/browser/renderer_host/media/audio_input_renderer_host.cc
diff --git a/content/browser/renderer_host/media/audio_input_renderer_host.cc b/content/browser/renderer_host/media/audio_input_renderer_host.cc
index 2698f7e2fd488a2c2a47d15b28ddb13b1958b7b1..568eb0eddf058623c851f68cc07f2166a7fc6957 100644
--- a/content/browser/renderer_host/media/audio_input_renderer_host.cc
+++ b/content/browser/renderer_host/media/audio_input_renderer_host.cc
@@ -436,6 +436,12 @@ void AudioInputRendererHost::DoCreateStream(
   // entry and construct an AudioInputController.
   entry->writer.reset(writer.release());
   if (WebContentsMediaCaptureId::IsWebContentsDeviceId(device_id)) {
+    // For MEDIA_DESKTOP_AUDIO_CAPTURE, the source is selected from picker
+    // window, we do not mute the source audio.
+    // For MEDIA_TAB_AUDIO_CAPTURE, the probable use case is Cast, we mute
+    // the source audio.
+    // TODO(qiangchen): Analyze audio constraints to make a duplicating or
+    // diverting decision. It would give web developer more flexibility.
     entry->controller = media::AudioInputController::CreateForStream(
         audio_manager_->GetTaskRunner(),
         this,
@@ -443,7 +449,8 @@ void AudioInputRendererHost::DoCreateStream(
             device_id,
             audio_params,
             audio_manager_->GetWorkerTaskRunner(),
-            audio_mirroring_manager_),
+            audio_mirroring_manager_,
+            type == MEDIA_DESKTOP_AUDIO_CAPTURE),
         entry->writer.get(),
         user_input_monitor_);
     // Only count for captures from desktop media picker dialog.