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() {
+  DCHECK(!g_instance);
+  g_instance = this;
+}
+
+DeviceClient::~DeviceClient() { g_instance = NULL; }

[Ken Rockot(use gerrit already), 2014/08/28 21:47:03]

I think it's preferable to use newlines when there's a non-empty body. Only
common exception is class-inlined code.

Technically not a strict style guide violation, but I've had complaints about
this in the past and tend to agree.

[Reilly Grant (use Gerrit), 2014/08/28 22:16:13]

Done.

+
+/* static */ DeviceClient* DeviceClient::Get() {

[Ken Rockot(use gerrit already), 2014/08/28 21:47:03]

// static

[Reilly Grant (use Gerrit), 2014/08/28 22:16:13]

Done.

+  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.
+  NOTREACHED();
+  return NULL;
+}
+
+}  // namespace device