Fix flaky video-controls-timeline layout test

This CL changes the fullscreen/video-controls-timeline.html layout test
to wait for the "seeked" event on the video instead of just the
"mouseup" event on the timeline to ensure that the video has updated
correctly to match the expected image.

Bug: 836241
Change-Id: Ia9a846db3eaba1452be3c21205f815da8f29893e
Reviewed-on: https://chromium-review.googlesource.com/1038762
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555251}
diff --git a/third_party/WebKit/LayoutTests/TestExpectations b/third_party/WebKit/LayoutTests/TestExpectations
index 6d31e4f..c6af26b 100644
--- a/third_party/WebKit/LayoutTests/TestExpectations
+++ b/third_party/WebKit/LayoutTests/TestExpectations
@@ -4628,7 +4628,6 @@
 crbug.com/831796 virtual/mouseevent_fractional/fast/events/autoscroll-in-textfield.html [ Failure Pass ]
 
 # Sheriff 2018-04-24
-crbug.com/836241 [ Linux ] virtual/android/fullscreen/video-controls-timeline.html [ Pass Failure ]
 crbug.com/836242 [ Linux Mac Win ] fast/loader/reload-zero-byte-plugin.html [ Pass Failure ]
 crbug.com/836275 [ Linux Mac ] fast/spatial-navigation/snav-two-elements-one-line.html [ Pass Failure ]
 
diff --git a/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline-expected.txt b/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline-expected.txt
index 03e6429..83934d5 100644
--- a/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline-expected.txt
+++ b/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline-expected.txt
@@ -4,5 +4,6 @@
 EVENT(webkitfullscreenchange)
 EVENT(mousedown)
 EVENT(mouseup)
+EVENT(seeked)
 END OF TEST
 
diff --git a/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline.html b/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline.html
index 5108313..ba197b16 100644
--- a/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline.html
+++ b/third_party/WebKit/LayoutTests/fullscreen/video-controls-timeline.html
@@ -22,7 +22,8 @@
                 waitForEvent(timeline, 'mousedown');
                 eventSender.mouseDown();
 
-                waitForEventAndEnd(timeline, 'mouseup');
+                waitForEvent(timeline, 'mouseup');
+                waitForEventAndEnd(video, 'seeked');
                 eventSender.mouseUp();
             }
             else