Update expecation for fast/dom/timer-throttling-out-of-view-cross-origin-page.html

fast/dom/timer-throttling-out-of-view-cross-origin-page.html is flaky

TBR=creis@chromium.org

Bug: 971590
Change-Id: Iaf70ef9df1ce6224882ed898538d6b3814746efe
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1647649
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666630}

third_party/blink/web_tests/TestExpectations

@@ -5786,3 +5786,6 @@ crbug.com/971252 [ Mac ] external/wpt/media-source/mediasource-play.html [ Pass
 crbug.com/971259 media/controls/volumechange-stopimmediatepropagation.html [ Pass Failure ]
 crbug.com/971262 http/tests/devtools/profiler/live-line-level-heap-profile.js [ Pass Timeout ]
 crbug.com/971319 [ Mac ] media/audio-garbage-collect.html [ Pass Timeout ]
+
+# Sheriff 2019-06-06
+crbug.com/971590 fast/dom/timer-throttling-out-of-view-cross-origin-page.html [ Pass Failure ]