Fix sensors layout tests flakiness

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

 'use strict';
 
 // Run a set of tests for a given |sensorType|. |updateReading| is
 // a called by the test to provide the mock values for sensor. |verifyReading|
 // is called so that the value read in JavaScript are the values expected (the ones
 // sent by |updateReading|).
 function runGenericSensorTests(sensorType, updateReading, verifyReading) {
   test(() => assert_throws(
     new RangeError(),
     () => new sensorType({frequency: -60})),
@@ skipping 292 matching lines @@
                   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.
                 // 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);
+                assert_approx_equals(fastSensorNotifiedCounter, elapsedUpdates, 1);
                 fastSensor.stop();
                 slowSensor.stop();
                 resolve(mockSensor);
               }
             }, reject);
 
             fastSensor.onchange = fastSensorWrapper.callback;
             slowSensor.onchange = slowSensorWrapper.callback;
             fastSensor.onerror = reject;
             slowSensor.onerror = reject;
           });
         })
         .then(mockSensor => { return mockSensor.removeConfigurationCalled(); });
 
     return testPromise;
   }
 
   sensor_test(sensor => {
     return checkFrequencyHintWorks(sensor);
   }, 'Test that frequency hint works (onchange reporting).');
 
   sensor_test(sensor => {
     sensor.mockSensorProvider.setContinuousReportingMode();
     return checkFrequencyHintWorks(sensor);
   }, 'Test that frequency hint works (continuous reporting).');
 }