Mark virtual/android/fullscreen/video-controls-timeline.html flaky on linux

TBR=thestig@chromium.org
NOTRY=true

Bug: 836241
Change-Id: Idfe38c1419121cbf99295d54aa3bf059a84a0359
Reviewed-on: https://chromium-review.googlesource.com/1025957Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553104}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4115,3 +4115,4 @@ crbug.com/831796 virtual/mouseevent_fractional/fast/events/autoscroll-in-textfie
 # Sheriff 2018-04-24
 crbug.com/836185 [ Mac10.11 Debug ] external/wpt/web-animations/animation-model/animation-types/addition-per-property.html [ Crash ]
 crbug.com/836185 [ Mac10.11 Debug ] external/wpt/web-animations/animation-model/animation-types/interpolation-per-property.html [ Crash ]
+crbug.com/836241 [ Linux ] virtual/android/fullscreen/video-controls-timeline.html [ Pass Failure ]