MidiScheduler binds to task runner of constructing thread

media/midi/midi_manager_usb.cc

Index: media/midi/midi_manager_usb.cc
diff --git a/media/midi/midi_manager_usb.cc b/media/midi/midi_manager_usb.cc
index e3e74aae386b6f4e26153170f3c3d464c0a4311f..ddd54c214996cb4fdd894ae72cd701e28ba81ced 100644
--- a/media/midi/midi_manager_usb.cc
+++ b/media/midi/midi_manager_usb.cc
@@ -19,6 +19,8 @@ MidiManagerUsb::MidiManagerUsb(std::unique_ptr<UsbMidiDevice::Factory> factory)
     : device_factory_(std::move(factory)) {}
 
 MidiManagerUsb::~MidiManagerUsb() {
+  base::AutoLock auto_lock(scheduler_lock_);
+  CHECK(!scheduler_);
 }
 
 void MidiManagerUsb::StartInitialization() {
@@ -26,9 +28,20 @@ void MidiManagerUsb::StartInitialization() {
       base::Bind(&MidiManager::CompleteInitialization, base::Unretained(this)));
 }
 
+void MidiManagerUsb::Finalize() {
+  // Destruct MidiScheduler on Chrome_IOThread.
+  base::AutoLock auto_lock(scheduler_lock_);
+  scheduler_.reset();
+}
+
 void MidiManagerUsb::Initialize(base::Callback<void(Result result)> callback) {
   initialize_callback_ = callback;
-  scheduler_.reset(new MidiScheduler(this));
+
+  {
+    base::AutoLock auto_lock(scheduler_lock_);
+    scheduler_.reset(new MidiScheduler(this));
+  }
+
   // This is safe because EnumerateDevices cancels the operation on destruction.
   device_factory_->EnumerateDevices(
       this,