Makes AudioOutputProxy -> AudioOutputDispatcher reference weak.

media/audio/audio_output_dispatcher_impl.cc

 // 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.
 
 #include "media/audio/audio_output_dispatcher_impl.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
@@ skipping 16 matching lines @@
                    close_delay,
                    this,
                    &AudioOutputDispatcherImpl::CloseAllIdleStreams),
       audio_log_(
           audio_manager->CreateAudioLog(AudioLogFactory::AUDIO_OUTPUT_STREAM)),
       audio_stream_id_(0) {}
 
 AudioOutputDispatcherImpl::~AudioOutputDispatcherImpl() {
   CHECK(task_runner_->BelongsToCurrentThread());
 
+  // Stop all active streams.
+  for (auto iter = proxy_to_physical_map_.begin();
+       iter != proxy_to_physical_map_.end();) {
+    // Note: Stopping the stream will invalidate the iterator.
+    // Increment the iterator before stopping the stream.
+    AudioOutputProxy* stream_proxy = iter->first;
+    ++iter;
+    StopStream(stream_proxy);

[alokp, 2017/01/10 20:33:59]

Do you think it is worthwhile to trigger AudioSourceCallback::OnError to notify
the clients that playback will stop?

IMO it is probably not worth because the browser is already shutting down.

[DaleCurtis, 2017/01/10 20:54:41]

No, this should be fine. Also, just use a for each style loop instead?

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

I cannot use the for-each style because StopStream would invalidate the
iterator. Note the comment.

[DaleCurtis, 2017/01/10 22:59:05]

Hmm, for some reason I thought for-each is immune to iterator invalidation since
it's not really an iterator. I'll have to go back and check.

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

AFAICT none - for_each or c++11 range-based for-loop - do not guarantee iterator
to be valid:
http://en.cppreference.com/w/cpp/language/range-for
http://en.cppreference.com/w/cpp/algorithm/for_each

In fact the possible implementation provided in the documentation would clearly
not work.

+  }
+
   // Close all idle streams immediately.  The |close_timer_| will handle
   // invalidating any outstanding tasks upon its destruction.
   CloseAllIdleStreams();
 
-  // There must be no idle proxy streams.
-  CHECK_EQ(idle_proxies_, 0u);
-
   // There must be no active proxy streams.
   CHECK(proxy_to_physical_map_.empty());
 
   // All idle physical streams must have been closed during shutdown.
   CHECK(idle_streams_.empty());
 }
 
 bool AudioOutputDispatcherImpl::OpenStream() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
@@ skipping 117 matching lines @@
 
     AudioStreamIDMap::iterator it = audio_stream_ids_.find(stream);
     DCHECK(it != audio_stream_ids_.end());
     audio_log_->OnClosed(it->second);
     audio_stream_ids_.erase(it);
   }
   idle_streams_.erase(idle_streams_.begin() + keep_alive, idle_streams_.end());
 }
 
 }  // namespace media