Implement the content/renderer and content/browser part of the Device Motion API.

content/common/device_motion_hardware_buffer.h

Index: content/common/device_motion_hardware_buffer.h
diff --git a/content/common/device_motion_hardware_buffer.h b/content/common/device_motion_hardware_buffer.h
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+++ b/content/common/device_motion_hardware_buffer.h
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+// Copyright (c) 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_COMMON_DEVICE_MOTION_HARDWARE_BUFFER_H_
+#define CONTENT_COMMON_DEVICE_MOTION_HARDWARE_BUFFER_H_
+
+#include "content/common/gamepad_seqlock.h"
+#include "third_party/WebKit/Source/Platform/chromium/public/WebDeviceMotionData.h"
+
+namespace content {
+
+// This structure is stored in shared memory that's shared between the browser
+// which does the hardware polling, and the consumers of the device motion
+// data, i.e. the renderers. 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.
+
+struct DeviceMotionHardwareBuffer {
+  GamepadSeqLock sequence;
+  WebKit::WebDeviceMotionData buffer;
+
+  // This boolean flag indicates that the values in the buffer are reliable and
+  // ready for reading. This is needed in cases where no motion information is
+  // available, but the event should be fired anyway (with null values)
+  // according to spec: http://dev.w3.org/geo/api/spec-source-orientation.html.
+  bool is_ready_for_read;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_DEVICE_MOTION_HARDWARE_BUFFER_H_