[Sensors] Simplify calculation of the reporting period

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

Index: third_party/WebKit/Source/modules/sensor/SensorProxy.cpp
diff --git a/third_party/WebKit/Source/modules/sensor/SensorProxy.cpp b/third_party/WebKit/Source/modules/sensor/SensorProxy.cpp
index a4087b399489f35c1bad22660326842d1f49c069..cf0348f71c344ce6c4e161c149e5d1893b50f58e 100644
--- a/third_party/WebKit/Source/modules/sensor/SensorProxy.cpp
+++ b/third_party/WebKit/Source/modules/sensor/SensorProxy.cpp
@@ -123,10 +123,11 @@ void SensorProxy::UpdateSensorReading() {
   }
 
   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();
   }
 }