Add new InputDeviceManager interface.

ui/events/devices/input_device_manager.cc

+// Copyright 2016 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 "ui/events/devices/input_device_manager.h"
+
+namespace ui {
+
+InputDeviceManager* InputDeviceManager::instance_ = nullptr;
+
+// static
+InputDeviceManager* InputDeviceManager::GetInstance() {
+  DCHECK(instance_);
+  return instance_;
+}
+
+// static
+bool InputDeviceManager::HasInstance() {
+  return instance_ != nullptr;
+}
+
+// static
+void InputDeviceManager::SetInstance(InputDeviceManager* instance) {
+  DCHECK(!instance_);
+  instance_ = instance;
+}
+
+// static
+void InputDeviceManager::ClearInstance() {
+  instance_ = nullptr;
+}
+
+}  // namespace ui