device: Cleanup class/struct forward declarations

device/generic_sensor/platform_sensor_ambient_light_mac.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 DEVICE_GENERIC_PLATFORM_SENSOR_AMBIENT_LIGHT_SENSOR_MAC_H_
 #define DEVICE_GENERIC_PLATFORM_SENSOR_AMBIENT_LIGHT_SENSOR_MAC_H_
 
 #include <IOKit/IOKitLib.h>
 
 #include "base/mac/scoped_ionotificationportref.h"
 #include "base/mac/scoped_ioobject.h"
 #include "device/generic_sensor/platform_sensor.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}
-
 namespace device {
 
 // Implementation of PlatformSensor for macOS to query the ambient light sensor.
 // This is a single instance object per browser process which is created by
 // The singleton PlatformSensorProviderMac. If there are no clients, this
 // instance is not created.
 class PlatformSensorAmbientLightMac : public PlatformSensor {
  public:
   // Construct a platform sensor of |type| AMBIENT_LIGHT, given
   // a buffer |mapping| to write the result back. |task_runner| is
@@ skipping 32 matching lines @@
   // sensor is busy.
   base::mac::ScopedIOObject<io_object_t> light_sensor_busy_notification_;
   double current_lux_;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformSensorAmbientLightMac);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_GENERIC_PLATFORM_SENSOR_AMBIENT_LIGHT_SENSOR_MAC_H_