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

content/common/shared_memory_seqlock_buffer.h

Index: content/common/shared_memory_seqlock_buffer.h
diff --git a/content/common/shared_memory_seqlock_buffer.h b/content/common/shared_memory_seqlock_buffer.h
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index 0000000000000000000000000000000000000000..5ac559bcefbebe52eae5bc41682d170a85eecb19
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+++ b/content/common/shared_memory_seqlock_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_SHARED_MEMORY_SEQLOCK_BUFFER_H_
+#define CONTENT_COMMON_SHARED_MEMORY_SEQLOCK_BUFFER_H_
+
+#include "content/common/one_writer_seqlock.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 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.
+
+template<class Data>
+class SharedMemorySeqLockBuffer {
+ public:
+  OneWriterSeqLock seqlock;
+  Data data;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_SHARED_MEMORY_SEQLOCK_BUFFER_H_