[sensors] PlatformSensorProvider implementations are notified when there are no sensor instances

device/generic_sensor/fake_platform_sensor_provider.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_FAKE_PLATFORM_SENSOR_PROVIDER_H_
 #define DEVICE_GENERIC_SENSOR_FAKE_PLATFORM_SENSOR_PROVIDER_H_
 
 #include "device/generic_sensor/platform_sensor_provider.h"
+#include "testing/gmock/include/gmock/gmock.h"
 
 namespace device {
 
 class FakePlatformSensorProvider : public PlatformSensorProvider {
  public:
   FakePlatformSensorProvider();
   ~FakePlatformSensorProvider() override;
 
-  static FakePlatformSensorProvider* GetInstance();
+  MOCK_METHOD0(AllSensorsRemoved, void());
 
  protected:
   void CreateSensorInternal(mojom::SensorType type,
                             mojo::ScopedSharedBufferMapping mapping,
                             const CreateSensorCallback& callback) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FakePlatformSensorProvider);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_GENERIC_SENSOR_MOCK_PLATFORM_SENSOR_PROVIDER_H_