Update audio renderer to stop transcribing muted audio

Bug: 1107940
Change-Id: I10b1790f120af7470086bf47709c145e788acbf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2477477Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Evan Liu <evliu@google.com>
Cr-Commit-Position: refs/heads/master@{#817776}

media/renderers/audio_renderer_impl.cc

@@ -959,7 +959,7 @@ bool AudioRendererImpl::HandleDecodedBuffer_Locked(
       first_packet_timestamp_ = buffer->timestamp();
 
 #if !defined(OS_ANDROID)
-    if (transcribe_audio_callback_)
+    if (transcribe_audio_callback_ && volume_ > 0)
       transcribe_audio_callback_.Run(buffer);
 #endif