[DeviceLight] Add renderer+common parts

content/common/device_sensors/device_light_data.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_COMMON_DEVICE_SENSORS_DEVICE_LIGHT_DATA_H_
+#define CONTENT_COMMON_DEVICE_SENSORS_DEVICE_LIGHT_DATA_H_
+
+#include "content/common/content_export.h"
+
+namespace content {
+
+// This struct is intentionally POD and fixed size so that it can be stored
+// in shared memory between the browser and the renderer processes.
+// POD class should be a struct, should have an inline cstor that uses
+// initializer lists and no dstor.
+struct DeviceLightData {
+  CONTENT_EXPORT DeviceLightData() : value(-1), valueIsUpdated(true) {}
+
+  double value;
+  bool valueIsUpdated;

[dcheng, 2014/06/16 17:14:08]

I don't understand the purpose of valueIsUpdated. The patch mentions that the
synchronization method will be mentioned in device_light_hardware_buffer.h, but
I don't see any further information about it. I think it would be most natural
to keep a copy of the last seen data and fire the event if data_.value !=
data.value. That way you don't need the bool at all?

Also, this should be named value_is_updated... if it's needed.

[riju_, 2014/06/18 09:26:01]

Done.

+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_DEVICE_SENSORS_DEVICE_LIGHT_DATA_H_