device: Cleanup class/struct forward declarations

device/generic_sensor/platform_sensor_android.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_SENSOR_PLATFORM_SENSOR_ANDROID_H_
 #define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_ANDROID_H_
 
 #include "device/generic_sensor/platform_sensor.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/memory/ref_counted.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}
-
 namespace device {
 
 class PlatformSensorAndroid : public PlatformSensor {
  public:
   // Register C++ methods exposed to Java using JNI.
   static bool RegisterJNI(JNIEnv* env);
 
   PlatformSensorAndroid(mojom::SensorType type,
                         mojo::ScopedSharedBufferMapping mapping,
                         PlatformSensorProvider* provider,
@@ skipping 23 matching lines @@
 
  private:
   // Java object org.chromium.device.sensors.PlatformSensor
   base::android::ScopedJavaGlobalRef<jobject> j_object_;
   DISALLOW_COPY_AND_ASSIGN(PlatformSensorAndroid);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_ANDROID_H_