Move gamepad_service out of content/ and into device/

device/gamepad/gamepad_shared_buffer.h

 // Copyright (c) 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_GAMEPAD_SHARED_BUFFER_H_
 #define DEVICE_GAMEPAD_SHARED_BUFFER_H_
 
 #include "base/memory/shared_memory.h"
+#include "device/base/synchronization/shared_memory_seqlock_buffer.h"
 #include "device/gamepad/gamepad_export.h"
 #include "third_party/WebKit/public/platform/WebGamepads.h"
 
 namespace device {
 
+/*
+
+ GamepadHardwareBuffer is stored in shared memory that's shared between the
+ browser which does the hardware polling, and the various consumers of the
+ gamepad state (renderers and NaCl plugins). The performance characteristics are
+ that we want low latency (so would like to avoid explicit communication via IPC
+ between producer and consumer) and relatively large data size.
+
+ Writer and reader operate on the same buffer assuming contention is low, and
+ contention is detected by using the associated SeqLock.
+
+*/
+
+typedef SharedMemorySeqLockBuffer<blink::WebGamepads> GamepadHardwareBuffer;
+
 class DEVICE_GAMEPAD_EXPORT GamepadSharedBuffer {
  public:
-  virtual ~GamepadSharedBuffer() {}
+  GamepadSharedBuffer();
+  ~GamepadSharedBuffer();
 
-  virtual base::SharedMemory* shared_memory() = 0;
-  virtual blink::WebGamepads* buffer() = 0;
+  base::SharedMemory* shared_memory();
+  blink::WebGamepads* buffer();
+  GamepadHardwareBuffer* hardware_buffer();
 
-  virtual void WriteBegin() = 0;
-  virtual void WriteEnd() = 0;
+  void WriteBegin();
+  void WriteEnd();
+
+ private:
+  base::SharedMemory shared_memory_;
+  GamepadHardwareBuffer* hardware_buffer_;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_GAMEPAD_SHARED_BUFFER_H_