Remove BrowserThread dependency from usb_service.

device/common/device_client.cc

+// Copyright 2014 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/common/device_client.h"
+
+#include "base/logging.h"
+
+namespace device {
+
+namespace {
+
+DeviceClient* g_instance = NULL;
+
+}  // namespace
+
+DeviceClient::DeviceClient() { g_instance = this; }

[Lei Zhang, 2014/08/28 18:44:57]

DCHECK |g_instance| is NULL first?

+
+DeviceClient::~DeviceClient() { g_instance = NULL; }
+
+/* static */ DeviceClient* DeviceClient::Get() {
+  DCHECK(g_instance);
+  return g_instance;
+}
+
+usb_service::UsbService* DeviceClient::GetUsbService() {
+  // This should never be called by clients which do not support the USB API.
+  NOTIMPLEMENTED();

[Lei Zhang, 2014/08/28 18:44:57]

This should be NOTREACHED(). NOTIMPLEMENTED() implies you want to actually
implement something here eventually.

+  return NULL;
+}
+
+}  // namespace device