video-poster-image-load-outlives-gc-without-crashing.html is flaky

See https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=http%2Ftests%2Fmisc%2Fvideo-poster-image-load-outlives-gc-without-crashing.html&testType=webkit_layout_tests.

Bug: 737959
TBR: petermayo@chromium.org
Change-Id: I02e5df4f2c9738b89318ab0da00ea370697395af
Reviewed-on: https://chromium-review.googlesource.com/555490
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Peter Mayo <petermayo@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483360}

third_party/WebKit/LayoutTests/TestExpectations

@@ -2950,6 +2950,8 @@ crbug.com/v8/6504 fast/js/mozilla/strict/B.1.2.html [ NeedsManualRebaseline ]
 crbug.com/v8/6529 inspector/console/console-dir.html [ NeedsManualRebaseline ]
 crbug.com/v8/6529 inspector/console/console-format.html [ NeedsManualRebaseline ]
 
+crbug.com/737959 http/tests/misc/video-poster-image-load-outlives-gc-without-crashing.html [ Failure Pass Crash ]
+
 # These tests are failing on Mac-10.12 when using an Intel GPU.
 crbug.com/736177 [ Mac ] css2.1/t1202-counter-04-b.html [ Failure Pass ]
 crbug.com/736177 [ Mac ] css2.1/t1202-counters-04-b.html [ Failure Pass ]