Use standardized and extendable accelerometer update type.

chromeos/accelerometer/accelerometer_types.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 CHROMEOS_ACCELEROMETER_ACCELEROMETER_TYPES_H_
+#define CHROMEOS_ACCELEROMETER_ACCELEROMETER_TYPES_H_
+
+#include "base/macros.h"
+#include "ui/gfx/geometry/vector3d_f.h"
+
+namespace chromeos {
+
+enum AccelerometerSource {
+  // Accelerometer is located in the device's screen. In the screen's natural
+  // orientation, positive X points to the right, consistent with the pixel
+  // position. Positive Y points up the screen. Positive Z is perpendicular to
+  // the screen, pointing outwards towards the user. The orientation is
+  // described at:
+  // http://www.html5rocks.com/en/tutorials/device/orientation/.
+  ACCELEROMETER_SOURCE_SCREEN = 0,
+
+  // Accelerometer is located in a keyboard attached to the device's screen.
+  // If the device is open 180 degrees the orientation is consistent with the
+  // screen. I.e. Positive X points to the right, positive Y points up on the
+  // keyboard and positive Z is perpendicular to the keyboard pointing out
+  // towards the user.
+  ACCELEROMETER_SOURCE_ATTACHED_KEYBOARD,
+
+  ACCELEROMETER_SOURCE_COUNT
+};
+
+struct AccelerometerReading {
+  AccelerometerReading() : present(false) {}

[Daniel Erat, 2014/08/28 00:27:07]

i suspect that this struct needs an explicit c'tor and d'tor in a .cc file:
http://www.chromium.org/developers/coding-style/cpp-dos-and-donts#TOC-Stop-in....

[flackr, 2014/08/28 01:21:37]

Done.

+
+  // If true, this accelerometer is being updated.
+  bool present;
+
+  // The reading from this accelerometer measured in m/s^2.
+  gfx::Vector3dF reading;
+};
+
+// An accelerometer update contains the last known value for each of the
+// accelerometers present on the device.
+class AccelerometerUpdate {
+ public:
+  AccelerometerUpdate() {}

[Daniel Erat, 2014/08/28 00:27:07]

same here

[flackr, 2014/08/28 01:21:36]

Done.

+
+  // Returns true if |source| has a valid value in this update.
+  bool has(AccelerometerSource source)  const {
+    return data_[source].present;
+  }
+
+  // Returns the last known value for |source|.
+  const gfx::Vector3dF& get(AccelerometerSource source) const {
+    return data_[source].reading;
+  }
+
+  void Set(AccelerometerSource source, float x, float y, float z) {
+    data_[source].present = true;
+    data_[source].reading.set_x(x);
+    data_[source].reading.set_y(y);
+    data_[source].reading.set_z(z);
+  }
+
+ protected:
+  AccelerometerReading data_[ACCELEROMETER_SOURCE_COUNT];
+
+  DISALLOW_COPY_AND_ASSIGN(AccelerometerUpdate);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_ACCELEROMETER_ACCELEROMETER_TYPES_H_