[Sensors] Simplify calculation of the reporting period

third_party/WebKit/LayoutTests/sensor/resources/sensor-helpers.js

 'use strict';
 
 // Wraps callback and calls reject_func if callback throws an error.
 class CallbackWrapper {
   constructor(callback, reject_func) {
     this.wrapper_func_ = (args) => {
       try {
         callback(args);
       } catch(e) {
         reject_func(e);
@@ skipping 180 matching lines @@
 
       startReading() {
         if (this.update_reading_function_ != null) {
           this.stopReading();
           let max_frequency_used =
               this.active_sensor_configurations_[0].frequency;
           let timeout = (1 / max_frequency_used) * 1000;
           this.sensor_reading_timer_id_ = window.setInterval(() => {
             if (this.update_reading_function_) {
               this.update_reading_function_(this.buffer_);
+              // For all tests sensor reading should have monotonically
+              // increasing timestamp in seconds.
+              this.buffer_[1] = window.performance.now() * 0.001;
               this.reading_updates_count_++;
             }
             if (this.reporting_mode_ === sensor.ReportingMode.ON_CHANGE) {
               this.client_.sensorReadingChanged();
             }
           }, timeout);
         }
       }
 
       stopReading() {
@@ skipping 164 matching lines @@
     };
 
     let onFailure = error => {
       sensor.mockSensorProvider.reset();
       return new Promise((resolve, reject) => { setTimeout(() => {reject(error);}, 0); });
     };
 
     return Promise.resolve(func(sensor)).then(onSuccess, onFailure);
   }), name, properties);
 }