[sensors] Introduce Generic Sensor API interfaces

device/sensors/public/interfaces/sensor.mojom

Index: device/sensors/public/interfaces/sensor.mojom
diff --git a/device/sensors/public/interfaces/sensor.mojom b/device/sensors/public/interfaces/sensor.mojom
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index 0000000000000000000000000000000000000000..adbf7396fb3b301b0895cc376a22593d417c4550
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+// Copyright 2016 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.
+
+module device.mojom;
+
+// Types of supported sensors
+enum SensorType {
+  FIRST = 1,
+  AMBIENT_LIGHT = FIRST,
+  PROXIMITY,
+  ACCELEROMETER,
+  GYROSCOPE,
+  PRESSURE,
+  LAST = PRESSURE // Note: LAST is also equal to the types count.
+};
+
+// Reporting mode supported by the Sensor.
+// ON_CHANGE  - client will be notified through OnSensorReadingChanged() signal
+//              whenever sensor reading is changed.
+// CONTINUOUS - sensor will continuously update its reading with frequency
+//              specified in SensorConfiguration.frequency.
+//              OnSensorReadingChanged() signal is not sent to the client for
+//              sensors with CONTINUOUS reporting mode.
+enum ReportingMode {
+  ON_CHANGE,
+  CONTINUOUS
+};
+
+struct SensorConfiguration {
+  // Frequency in Hz
+  double frequency;

[Tom Sepez, 2016/07/11 17:40:03]

Are there better limits for this than just the range of a double?  What happens
if we ask to poll for example, at GHz or above or conversely at extremely low
rates?  What does a negative frequency mean?  Do all implementations have to
check these?

[Mikhail, 2016/07/12 08:26:50]

Here we cap frequency to 60Hz
https://codereview.chromium.org/2078433002/diff/200001/device/sensors/platfor...
Also an inappropriate configuration will raise an error on platform side.

+  // TODO(shalamov): Add map<string, union> for sensor specific configuration.
+};
+
+// Interface for controlling the Sensor.
+interface Sensor {
+  // Requests sensor to start reading sensor data with specified
+  // SensorConfiguration.
+  // Sensor holds the list of added configurations and it always polls
+  // the platform (and updates the shared buffer) at the maxiumum frequency
+  // among the obtained from the stored configurations, so that all clients
+  // can have sensor data in time.
+  AddConfiguration(SensorConfiguration configuration) => (bool success);
+
+  // Requests sensor to stop reading sensor data for specified
+  // SensorConfiguration.
+  // This call excludes |configuration| from the Sensor's list making it
+  // reconsider the the shared buffer udpate frequency. If there are no
+  // configurations left in the Sensor's configuration list it stops polling
+  // sensor data from the platform and update the shared buffer.
+  RemoveConfiguration(SensorConfiguration configuration) => (bool success);
+};
+
+// Interface that client of the Sensor interface must implement to observe
+// sensor reading changes and error conditions.
+interface SensorClient {
+  // Signals SensorClient when there is an error.
+  RaiseError();
+
+  // Signals SensorClient when reading has been changed (only for sensors with
+  // ReportingMode::ON_CHANGE).
+  SensorReadingChanged();
+};