[Sensors] Allow Sensor API only on secure top-level browsing contexts and add frequency checks

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 12 matching lines @@
 // 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 {
-  // Requested frequency in Hz (max is 60 Hz).
+  // Maximum allowed frequency is 60 Hz.
+  const double kMaxAllowedFrequency = 60.0;

[Tom Sepez, 2016/09/20 16:41:06]

nit: If we named this kMaxAllowedFrequencyHz, we could lose the comment entirel.

+
+  // Requested frequency in Hz.
   double frequency;
   // TODO(shalamov): Add map<string, union> for sensor specific configuration.
 };
 
 // Interface for controlling the Sensor.
 interface Sensor {
 
   // Requests sensor to provide its default configuration.
   GetDefaultConfiguration() => (SensorConfiguration configuration);
 
@@ skipping 31 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();
 };