Pass task runners to AudioManager constructor.

content/browser/browser_main_loop.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 "content/browser/browser_main_loop.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 1028 matching lines @@
   // On Mac and windows, the monitor needs to be destroyed on the same thread
   // as they were created. On Linux, the monitor will be deleted when IO thread
   // goes away.
 #if defined(OS_WIN)
   system_message_window_.reset();
 #elif defined(OS_MACOSX)
   device_monitor_mac_.reset();
 #endif
 #endif  // !defined(OS_IOS)
 
+  // Destroy audio_manager_ on audio thread.

[DaleCurtis, 2016/03/18 17:48:18]

Be careful here, this changes the destruction order of AudioManager relative to
it's current position.

[alokp, 2016/03/18 18:40:06]

Yeah I need to cycle this through the trybots.

+  AudioManager::Destroy(audio_manager_.release());
+
   // Shutdown Mojo shell and IPC.
 #if !defined(OS_IOS)
   mojo_shell_context_.reset();
   mojo_ipc_support_.reset();
 #endif
 
   // Must be size_t so we can subtract from it.
   for (size_t thread_id = BrowserThread::ID_COUNT - 1;
        thread_id >= (BrowserThread::UI + 1);
        --thread_id) {
@@ skipping 190 matching lines @@
       BrowserGpuMemoryBufferManager::current(), "BrowserGpuMemoryBufferManager",
       io_thread_->task_runner());
 #if defined(OS_ANDROID)
   base::trace_event::MemoryDumpManager::GetInstance()->RegisterDumpProvider(
       tracing::GraphicsMemoryDumpProvider::GetInstance(), "AndroidGraphics",
       nullptr);
 #endif
 
   {
     TRACE_EVENT0("startup", "BrowserThreadsStarted::Subsystem:AudioMan");
-    audio_manager_.reset(media::AudioManager::CreateWithHangTimer(
-        MediaInternals::GetInstance(), io_thread_->task_runner()));
+    scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner;

[DaleCurtis, 2016/03/18 17:48:18]

What will this code look like for cast? 

[alokp, 2016/03/18 18:40:06]

Since BML is common for all platforms/content-embedders, we cannot add any
cast-specific override here. I can think of two options:
1. [Not Good] Rely on BML passing NULL task_runner, which can be overridden in
CastAudioManagerFactory.

2. [Good] Add ContentBrowserClient::GetAudio[Worker]TaskRunner functions that we
can override. This approach is much cleaner. I think you missed one my comments
in AudioManager about making task runners non-optional. Copying it here:

We could make the task_runner arguments mandatory by creating the audio thread
in BrowserMainLoop. But then Cast needs a way to override it. One way to do that
would be to add ContentBrowserClient::GetAudioTaskRunner. The default
implementation will return NULL, in which case BML will create the audio thread.

ContentBrowserClient::GetAudioTaskRunner will work better for us and we will
also avoid the singleton AudioThread class but I am not sure if this function
belongs in ContentBrowserClient. We do have a
ContentBrowserClient::CreateCdmFactory, so maybe?

+    scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner;
+    scoped_refptr<base::SingleThreadTaskRunner> monitor_task_runner;
+    AudioLogFactory* audio_log_factory = MediaInternals::GetInstance();
+#if defined(OS_MACOSX)
+    // CoreAudio calls must occur on the main thread of the process, which in
+    // our case is sadly the browser UI thread. Failure to execute calls on the
+    // right thread leads to crashes and odd behavior.
+    // See http://crbug.com/158170.
+    // Since the audio thread is the UI thread, a hang monitor is not
+    // necessary or recommended.
+    audio_task_runner = base::ThreadTaskRunnerHandle::Get();
+#else
+    monitor_task_runner = io_thread_->task_runner();
+#endif
+    audio_manager_.reset(
+        media::AudioManager::Create(audio_task_runner, worker_task_runner,
+                                    monitor_task_runner, audio_log_factory));
   }
 
   {
     TRACE_EVENT0("startup", "BrowserThreadsStarted::Subsystem:MidiManager");
     midi_manager_.reset(media::midi::MidiManager::Create());
   }
 
 #if defined(OS_WIN)
   system_message_window_.reset(new media::SystemMessageWindowWin);
 #elif defined(OS_LINUX) && defined(USE_UDEV)
@@ skipping 210 matching lines @@
   DCHECK(is_tracing_startup_for_duration_);
 
   is_tracing_startup_for_duration_ = false;
   TracingController::GetInstance()->StopTracing(
       TracingController::CreateFileSink(
           startup_trace_file_,
           base::Bind(OnStoppedStartupTracing, startup_trace_file_)));
 }
 
 }  // namespace content