Windows: Retain initial IMMDeviceEnumerator throughout

Speculative fix for what looks like a race during CoreAudio
initialization. The device enumerator created to ensure for CoreAudio
availability is leaked rather than destroyed immediately after
construction.

Bug: 955434
Change-Id: Ifa70350691448ec6ba57c9eb2b93106aa8edf65b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584276Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Oskar Sundbom <ossu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654447}

media/audio/win/audio_manager_win.cc

@@ -149,9 +149,9 @@ AudioManagerWin::AudioManagerWin(std::unique_ptr<AudioThread> audio_thread,
                                  AudioLogFactory* audio_log_factory)
     : AudioManagerBase(std::move(audio_thread), audio_log_factory) {
   // |CoreAudioUtil::IsSupported()| uses static variables to avoid doing
-  // multiple initializations.  This is however not thread safe.
-  // So, here we call it explicitly before we kick off the audio thread
-  // or do any other work.
+  // multiple initializations. This is thread safe but call it here explicitly
+  // to ensure initialization is done on the main thread and before we do any
+  // other work.
   CoreAudioUtil::IsSupported();
 
   SetMaxOutputStreamsAllowed(kMaxOutputStreams);

media/audio/win/core_audio_util_win.cc

@@ -413,13 +413,13 @@ ChannelLayout GetChannelLayout(
   return channel_layout;
 }
 
-bool IsSupportedInternal() {
+IMMDeviceEnumerator* IsSupportedInternal() {
   // It is possible to force usage of WaveXxx APIs by using a command line
   // flag.
   const base::CommandLine* cmd_line = base::CommandLine::ForCurrentProcess();
   if (cmd_line->HasSwitch(switches::kForceWaveAudio)) {
     DVLOG(1) << "Forcing usage of Windows WaveXxx APIs";
-    return false;
+    return nullptr;
   }
 
   // Verify that it is possible to a create the IMMDeviceEnumerator interface.
@@ -430,10 +430,10 @@ bool IsSupportedInternal() {
     LOG(ERROR)
         << "Failed to create Core Audio device enumerator on thread with ID "
         << GetCurrentThreadId();
-    return false;
+    return nullptr;
   }
 
-  return true;
+  return device_enumerator.Detach();
 }
 
 // Retrieve an audio device specified by |device_id| or a default device
@@ -647,8 +647,10 @@ size_t CoreAudioUtil::WaveFormatWrapper::size() const {
 }
 
 bool CoreAudioUtil::IsSupported() {
-  static bool g_is_supported = IsSupportedInternal();
-  return g_is_supported;
+  // Hold on to the device enumerator throughout, to avoid multiple
+  // de-/initializations of CoreAudio. See: crbug.com/955434
+  static IMMDeviceEnumerator* g_enumerator = IsSupportedInternal();
+  return g_enumerator != nullptr;
 }
 
 // CoreAudioUtil implementation.