Send kStopMark from AudioOutputController to stop AudioThread in renderer

content/renderer/media/audio_device.cc

Index: content/renderer/media/audio_device.cc
===================================================================
--- content/renderer/media/audio_device.cc	(revision 131586)
+++ content/renderer/media/audio_device.cc	(working copy)
@@ -299,7 +299,8 @@
       memset(shared_memory.memory(), 0, memory_length_);
       media::SetActualDataSizeInBytes(&shared_memory, memory_length_, 0);
       continue;
-    } else if (pending_data < 0) {
+    } else if (pending_data == media::AudioOutputController::kStopMark ||
+               pending_data < 0) {
       break;
     }