Implement AudioOutputProxy.

media/audio/linux/audio_manager_linux.cc

Index: media/audio/linux/audio_manager_linux.cc
diff --git a/media/audio/linux/audio_manager_linux.cc b/media/audio/linux/audio_manager_linux.cc
index fdf80441bf37473946463082121643377138669d..e6c34e51c442bc3601d47e94fce2fa5d93f1c373 100644
--- a/media/audio/linux/audio_manager_linux.cc
+++ b/media/audio/linux/audio_manager_linux.cc
@@ -6,6 +6,7 @@
 
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "media/audio/audio_output_dispatcher.h"
 #include "media/audio/fake_audio_input_stream.h"
 #include "media/audio/fake_audio_output_stream.h"
 #include "media/audio/linux/alsa_input.h"
@@ -94,6 +95,11 @@ AudioManagerLinux::~AudioManagerLinux() {
   // This way we make sure activities of the audio streams are all stopped
   // before we destroy them.
   audio_thread_.Stop();
+
+  // Free output dispatchers first, so that they closes all streams that
+  // are still open.
+  output_dispatchers_.clear();
+
   active_streams_.clear();
 }