Fix "unused variable" warnings.

content/browser/device_sensors/data_fetcher_shared_memory.h

 // Copyright 2014 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 CONTENT_BROWSER_DEVICE_SENSORS_DATA_FETCHER_SHARED_MEMORY_H_
 #define CONTENT_BROWSER_DEVICE_SENSORS_DATA_FETCHER_SHARED_MEMORY_H_
 
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "content/browser/device_sensors/data_fetcher_shared_memory_base.h"
@@ skipping 27 matching lines @@
   ~DataFetcherSharedMemory() override;
 
 #if defined(OS_ANDROID)
   void Shutdown() override;
 #endif
 
  private:
   bool Start(ConsumerType consumer_type, void* buffer) override;
   bool Stop(ConsumerType consumer_type) override;
 
-#if !defined(OS_ANDROID)
-  DeviceMotionHardwareBuffer* motion_buffer_;
-  DeviceOrientationHardwareBuffer* orientation_buffer_;
-  DeviceOrientationHardwareBuffer* orientation_absolute_buffer_;
-  DeviceLightHardwareBuffer* light_buffer_;
+#if defined(OS_LINUX) || defined(OS_MACOSX) || defined(OS_WIN)
+#if !defined(OS_CHROMEOS)
+  DeviceMotionHardwareBuffer* motion_buffer_ = nullptr;
+  DeviceOrientationHardwareBuffer* orientation_buffer_ = nullptr;
+  DeviceLightHardwareBuffer* light_buffer_ = nullptr;
+#endif
+  DeviceOrientationHardwareBuffer* orientation_absolute_buffer_ = nullptr;
 #endif
 
 #if defined(OS_CHROMEOS)
   std::unique_ptr<SensorManagerChromeOS> sensor_manager_;
 #elif defined(OS_MACOSX)
   void Fetch(unsigned consumer_bitmask) override;
   FetcherType GetType() const override;
 
   std::unique_ptr<AmbientLightSensor> ambient_light_sensor_;
   std::unique_ptr<SuddenMotionSensor> sudden_motion_sensor_;
@@ skipping 16 matching lines @@
   base::win::ScopedComPtr<ISensor> sensor_gyrometer_;
   base::win::ScopedComPtr<ISensor> sensor_light_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(DataFetcherSharedMemory);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVICE_SENSORS_DATA_FETCHER_SHARED_MEMORY_H_