[Sensors] Improvements in shared buffer managing

device/generic_sensor/public/interfaces/sensor.mojom

 // 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,
@@ skipping 20 matching lines @@
 
 struct SensorConfiguration {
   // Maximum allowed frequency is 60 Hz.
   const double kMaxAllowedFrequency = 60.0;
 
   // Requested frequency in Hz.
   double frequency;
   // TODO(shalamov): Add map<string, union> for sensor specific configuration.
 };
 
+// Each sensor uses the following structure to provide reading data.
+struct SensorReading {
+  // Timestamp in seconds, obtained from system performance counter.
+  double timestamp;
+  // Sensor data fields.
+  double value1;
+  double value2;
+  double value3;
+};
+
 // Interface for controlling the Sensor.
 interface Sensor {
 
   // Requests sensor to provide its default configuration.
   GetDefaultConfiguration() => (SensorConfiguration configuration);
 
   // 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
@@ skipping 27 matching lines @@
 // 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();
 };