Implement PollingThread for Device Motion.

content/browser/device_orientation/device_motion_provider.h

 // Copyright 2013 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_ORIENTATION_DEVICE_MOTION_PROVIDER_H_
 #define CONTENT_BROWSER_DEVICE_ORIENTATION_DEVICE_MOTION_PROVIDER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
 #include "content/common/content_export.h"
 #include "content/common/device_motion_hardware_buffer.h"
 
 namespace content {
 class DataFetcherSharedMemory;
 
+// This class owns the shared memory buffer for Device Motion and makes
+// sure the data is fetched into that buffer.
+// When DataFetcherSharedMemory::NeedsPolling() is true, it starts a
+// background polling thread to make sure the data is fetched at regular
+// intervals.
 class CONTENT_EXPORT DeviceMotionProvider {
  public:
   DeviceMotionProvider();
+  explicit DeviceMotionProvider(scoped_ptr<DataFetcherSharedMemory> fetcher);
+
   virtual ~DeviceMotionProvider();
 
   // Returns the shared memory handle of the device motion data duplicated
   // into the given process.
   base::SharedMemoryHandle GetSharedMemoryHandleForProcess(
       base::ProcessHandle renderer_process);
 
-  // Pause and resume the background polling thread. Can be called from any
-  // thread.
   void StartFetchingDeviceMotionData();
   void StopFetchingDeviceMotionData();
 
  private:
-  base::SharedMemory device_motion_shared_memory_;
+  class PollingThread;
+
+  void Initialize();
+  void CreateAndStartPollingThread();
 
   DeviceMotionHardwareBuffer* SharedMemoryAsHardwareBuffer();
 
+  base::SharedMemory device_motion_shared_memory_;
   scoped_ptr<DataFetcherSharedMemory> data_fetcher_;
-
-  bool is_started_;
+  scoped_ptr<PollingThread> polling_thread_;
+  bool is_stopped_or_stopping_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceMotionProvider);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVICE_ORIENTATION_DEVICE_MOTION_PROVIDER_H_