Add browser tests for USB device add/remove events.

device/usb/usb_service.cc

+// Copyright 2015 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 "device/usb/usb_service.h"
+
+#include "base/message_loop/message_loop.h"
+#include "device/usb/usb_device.h"
+#include "device/usb/usb_service_impl.h"
+
+namespace device {
+
+namespace {
+
+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) {
+}
+
+void UsbService::Observer::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {
+}
+
+// static
+UsbService* UsbService::GetInstance(
+    scoped_refptr<base::SingleThreadTaskRunner> ui_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);
+  }
+  return g_service;
+}
+
+// static
+void UsbService::SetInstanceForTest(UsbService* instance) {
+  g_service = instance;
+  new Destroyer(instance);
+}
+
+UsbService::UsbService() {
+}
+
+UsbService::~UsbService() {
+}
+
+void UsbService::AddObserver(Observer* observer) {
+  DCHECK(CalledOnValidThread());
+  observer_list_.AddObserver(observer);
+}
+
+void UsbService::RemoveObserver(Observer* observer) {
+  DCHECK(CalledOnValidThread());
+  observer_list_.RemoveObserver(observer);
+}
+
+void UsbService::NotifyDeviceAdded(scoped_refptr<UsbDevice> device) {
+  DCHECK(CalledOnValidThread());
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceAdded(device));
+}
+
+void UsbService::NotifyDeviceRemoved(scoped_refptr<UsbDevice> device) {
+  DCHECK(CalledOnValidThread());
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemoved(device));
+}
+
+}  // namespace device