Move device/usb classes from the FILE thread to UI thread.

device/usb/usb_service.cc

Index: device/usb/usb_service.cc
diff --git a/device/usb/usb_service.cc b/device/usb/usb_service.cc
index 10338fc7e14e45f832ae342e43c2447d10604828..18732b50d3e14d581dca34d2641184e6b9cf7908 100644
--- a/device/usb/usb_service.cc
+++ b/device/usb/usb_service.cc
@@ -17,28 +17,6 @@ UsbService* g_service;
 
 }  // namespace
 
-// This class manages the lifetime of the global UsbService instance so that
-// it is destroyed when the current message loop is destroyed. A lazy instance
-// cannot be used because this object does not live on the main thread.
-class UsbService::Destroyer : private base::MessageLoop::DestructionObserver {
- public:
-  explicit Destroyer(UsbService* usb_service) : usb_service_(usb_service) {
-    base::MessageLoop::current()->AddDestructionObserver(this);
-  }
-  ~Destroyer() override {}
-
- private:
-  // base::MessageLoop::DestructionObserver implementation.
-  void WillDestroyCurrentMessageLoop() override {
-    base::MessageLoop::current()->RemoveDestructionObserver(this);
-    delete usb_service_;
-    delete this;
-    g_service = nullptr;
-  }
-
-  UsbService* usb_service_;
-};
-
 void UsbService::Observer::OnDeviceAdded(scoped_refptr<UsbDevice> device) {
 }
 
@@ -51,25 +29,23 @@ void UsbService::Observer::OnDeviceRemovedCleanup(
 
 // static
 UsbService* UsbService::GetInstance(
-    scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
+    scoped_refptr<base::SequencedTaskRunner> blocking_task_runner) {
   if (!g_service) {
-    g_service = UsbServiceImpl::Create(ui_task_runner);
-    // This object will clean itself up when the message loop is destroyed.
-    new Destroyer(g_service);
+    // UsbService constructor saves the pointer this returns and UsbServiceImpl
+    // will destroy itself when the current message loop exits.
+    UsbServiceImpl::Create(blocking_task_runner);
   }
   return g_service;
 }
 
-// static
-void UsbService::SetInstanceForTest(UsbService* instance) {
-  g_service = instance;
-  new Destroyer(instance);
-}
-
 UsbService::UsbService() {
+  DCHECK(!g_service);
+  g_service = this;
 }
 
 UsbService::~UsbService() {
+  DCHECK(g_service);
+  g_service = nullptr;
 }
 
 void UsbService::AddObserver(Observer* observer) {
@@ -85,18 +61,12 @@ void UsbService::RemoveObserver(Observer* observer) {
 void UsbService::NotifyDeviceAdded(scoped_refptr<UsbDevice> device) {
   DCHECK(CalledOnValidThread());
 
-  USB_LOG(USER) << "USB device added: vendorId = " << device->vendor_id()
-                << ", productId = " << device->product_id()
-                << ", uniqueId = " << device->unique_id();
-
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceAdded(device));
 }
 
 void UsbService::NotifyDeviceRemoved(scoped_refptr<UsbDevice> device) {
   DCHECK(CalledOnValidThread());
 
-  USB_LOG(USER) << "USB device removed: uniqueId = " << device->unique_id();
-
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemoved(device));
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemovedCleanup(device));
 }