Singletons changes necessary to run the UI Service inside the browser's process.

ui/events/devices/input_device_manager.h

 // 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.
 
 #ifndef UI_EVENTS_DEVICES_INPUT_DEVICE_MANAGER_H_
 #define UI_EVENTS_DEVICES_INPUT_DEVICE_MANAGER_H_
 
 #include <vector>
 
 #include "base/macros.h"
 #include "ui/events/devices/events_devices_export.h"
 #include "ui/events/devices/input_device.h"
 #include "ui/events/devices/input_device_event_observer.h"
 #include "ui/events/devices/touchscreen_device.h"
 
 namespace ui {
 
-// Interface to query available input devices. Holds a static pointer to an
-// implementation that provides this service. The implementation could be
+// Interface to query available input devices. Holds a thread-local pointer to
+// an implementation that provides this service. The implementation could be
 // DeviceDataManager or something that mirrors the necessary state if
 // DeviceDataManager is in a different process.
 class EVENTS_DEVICES_EXPORT InputDeviceManager {
  public:
   InputDeviceManager() {}
 
   static InputDeviceManager* GetInstance();
   static bool HasInstance();
 
   virtual const std::vector<InputDevice>& GetKeyboardDevices() const = 0;
   virtual const std::vector<TouchscreenDevice>& GetTouchscreenDevices()
       const = 0;
   virtual const std::vector<InputDevice>& GetMouseDevices() const = 0;
   virtual const std::vector<InputDevice>& GetTouchpadDevices() const = 0;
 
   virtual bool AreDeviceListsComplete() const = 0;
   virtual bool AreTouchscreensEnabled() const = 0;
 
   virtual void AddObserver(InputDeviceEventObserver* observer) = 0;
   virtual void RemoveObserver(InputDeviceEventObserver* observer) = 0;
 
  protected:
-  // Sets the instance. This should only be set once per process.
+  // Sets the instance. This should only be set once per thread.
   static void SetInstance(InputDeviceManager* instance);
 
   // Clears the instance. InputDeviceManager doesn't own the instance and won't
   // destroy it, so it should be cleared before it is destroyed elsewhere.
   static void ClearInstance();
 
  private:
   static InputDeviceManager* instance_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(InputDeviceManager);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_DEVICES_INPUT_DEVICE_MANAGER_H_