Makes AudioOutputProxy -> AudioOutputDispatcher reference weak.

media/audio/audio_output_dispatcher.h

 // 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.
 
 // AudioOutputDispatcher is a single-threaded base class that dispatches
 // creation and deletion of audio output streams. AudioOutputProxy objects use
 // this class to allocate and recycle actual audio output streams. When playback
 // is started, the proxy calls StartStream() to get an output stream that it
 // uses to play audio. When playback is stopped, the proxy returns the stream
 // back to the dispatcher by calling StopStream().
 //
 // AudioManagerBase creates one specialization of AudioOutputDispatcher on the
 // audio thread for each possible set of audio parameters. I.e streams with
 // different parameters are managed independently.  The AudioOutputDispatcher
 // instance is then deleted on the audio thread when the AudioManager shuts
 // down.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
 
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
 #include "media/base/audio_parameters.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace media {
 
 class AudioOutputProxy;
 
-class MEDIA_EXPORT AudioOutputDispatcher {
+class MEDIA_EXPORT AudioOutputDispatcher
+    : public base::SupportsWeakPtr<AudioOutputDispatcher> {

[DaleCurtis, 2017/01/10 20:54:40]

Instead of adding this can you make the constructor private and add a Create()
method which returns a WeakPtr? SupportsWeakPtr is a bit too permissive.

[alokp, 2017/01/10 22:51:26]

A Create method will not work because AMB still needs to hold a
unique_ptr<AudioOutputDispatcher>. We just need the WeakPtr for AOPs. I could
add a virtual AudioOutputDispatcher::GetWeakPtr, but I am not sure if it would
be any better than deriving from SupportsWeakPtr.

[DaleCurtis, 2017/01/10 22:58:08]

what about AOD::CreateProxy() which returns an AudioOutputProxy using the
internal WeakPtr?

[alokp, 2017/01/10 23:31:53]

Yes - this should work. Done.

  public:
   AudioOutputDispatcher(AudioManager* audio_manager,
                         const AudioParameters& params,
                         const std::string& device_id);
   virtual ~AudioOutputDispatcher();
 
   // Called by AudioOutputProxy to open the stream.
   // Returns false, if it fails to open it.
   virtual bool OpenStream() = 0;
 
@@ skipping 25 matching lines @@
   const AudioParameters params_;
   std::string device_id_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AudioOutputDispatcher);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_