[Sensors] Simplify calculation of the reporting period

third_party/WebKit/Source/modules/sensor/SensorProxy.cpp

 // 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.
 
 #include "modules/sensor/SensorProxy.h"
 
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/sensor/SensorProviderProxy.h"
 #include "platform/mojo/MojoHelper.h"
@@ skipping 105 matching lines @@
   const int kMaxReadAttemptsCount = 10;
   device::SensorReading reading_data;
   while (!TryReadFromBuffer(reading_data)) {
     if (++read_attempts == kMaxReadAttemptsCount) {
       HandleSensorError();
       return;
     }
   }
 
   if (reading_.timestamp != reading_data.timestamp) {
+    DCHECK_GT(reading_data.timestamp, reading_.timestamp)
+        << "Timestamps must increase monotonically";
     reading_ = reading_data;
-    double now = WTF::MonotonicallyIncreasingTime();
     for (Observer* observer : observers_)
-      observer->OnSensorReadingChanged(now);
+      observer->OnSensorReadingChanged();
   }
 }
 
 void SensorProxy::RaiseError() {
   HandleSensorError();
 }
 
 void SensorProxy::SensorReadingChanged() {
   DCHECK_EQ(ReportingMode::ON_CHANGE, mode_);
   UpdateSensorReading();
@@ skipping 133 matching lines @@
     // TODO(crbug/721297) : We need to find out an algorithm for resulting
     // polling frequency.
     polling_timer_.StartRepeating(1 / frequencies_used_.back(),
                                   BLINK_FROM_HERE);
   } else {
     polling_timer_.Stop();
   }
 }
 
 }  // namespace blink