test: Fix test expectations in StreamingEngine integration

This test case was to show that we don't seek when the app suppresses
gap jumping.  However, it set expectations based on time, and on Xbox
One, the platform plays all the way through the gap.  This broke our
time exepctations.

Instead of _inferring_ that we don't seek based on time, we should
directly measure seeking.  This is more robust to platform
differences.

Change-Id: I8a5227d3d33e9e87cab9872e3a61aa47ed1b332c

test/media/streaming_engine_integration.js

@@ -522,13 +522,20 @@ describe('StreamingEngine', () => {
       // readyState is 0.
       await waiter.timeoutAfter(5).waitForEvent(video, 'loadeddata');
 
+      let seekCount = 0;
+      eventManager.listen(video, 'seeking', () => {
+        seekCount++;
+      });
+
       video.currentTime = 8;
       video.play();
 
       await shaka.test.Util.delay(5);
-      // IE/Edge somehow plays inside the gap.  Just make sure we
-      // don't jump the gap.
-      expect(video.currentTime).toBeLessThan(20);
+
+      // IE/Edge somehow plays _into_ the gap, and Xbox One plays _through_ the
+      // gap.  Just make sure _we_ don't jump the gap by seeking.  One seek is
+      // required to start playback at time 8.
+      expect(seekCount).toBe(1);
     });
 
     /**