Use standardized and extendable accelerometer update type.

ui/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 UI_ACCEROMETER_ACCELEROMETER_TYPES_H_
+#define UI_ACCEROMETER_ACCELEROMETER_TYPES_H_
+
+#include "base/macros.h"
+#include "ui/accelerometer/ui_accelerometer_export.h"
+#include "ui/gfx/geometry/vector3d_f.h"
+
+namespace ui {
+
+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

[sky, 2014/08/29 02:15:27]

Don't we normally have positive y going down?

[flackr, 2014/08/29 03:09:52]

Normally we do at least in pixel space, but not in the device orientation spec
http://w3c.github.io/deviceorientation/spec-source-orientation.html#deviceori...
or Android SensorEvents
http://developer.android.com/reference/android/hardware/SensorEvent.html.

+  // 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 UI_ACCELEROMETER_EXPORT AccelerometerReading {
+  AccelerometerReading();
+  ~AccelerometerReading();
+
+  // 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 UI_ACCELEROMETER_EXPORT AccelerometerUpdate {
+ public:
+  AccelerometerUpdate();
+  ~AccelerometerUpdate();
+
+  // 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  // UI_ACCEROMETER_ACCELEROMETER_TYPES_H_