[Sensors] Reland: Align sensor reading updates and 'onchange' notification with rAF.

third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js

Index: third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js
diff --git a/third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js b/third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js
index ee5f312333cceab119156d79549531e72f380954..fc1fc8ed316a9d98204c4853717e2f68f9ba8f2a 100644
--- a/third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js
+++ b/third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js
@@ -291,6 +291,7 @@ function runGenericSensorTests(sensorType, updateReading, verifyReading) {
           return new Promise((resolve, reject) => {
             let fastSensorNotifiedCounter = 0;
             let slowSensorNotifiedCounter = 0;
+            let readingUpdatesCounter = 0;
 
             let fastSensorWrapper = new CallbackWrapper(() => {
               fastSensorNotifiedCounter++;
@@ -300,11 +301,16 @@ function runGenericSensorTests(sensorType, updateReading, verifyReading) {
               slowSensorNotifiedCounter++;
               if (slowSensorNotifiedCounter == 1) {
                   fastSensor.start();
+                  readingUpdatesCounter = mockSensor.reading_updates_count();
               } else if (slowSensorNotifiedCounter == 2) {
                 // By the moment slow sensor (9 Hz) is notified for the
                 // next time, the fast sensor (30 Hz) has been notified
                 // for int(30/9) = 3 times.
-                assert_equals(fastSensorNotifiedCounter, 3);
+                // In actual implementation updates are bound to rAF,
+                // (not to a timer) so fluctuations are possible, so we
+                // reference to the actual elapsed updates count.
+                let elapsedUpdates = mockSensor.reading_updates_count() - readingUpdatesCounter;
+                assert_equals(fastSensorNotifiedCounter, elapsedUpdates);
                 fastSensor.stop();
                 slowSensor.stop();
                 resolve(mockSensor);