Marked wrong test as flaky.

Correct autoplay test should be marked now.

TBR=mlamouri@chromium.org

Bug: 908347
Change-Id: I45c3b971769c8de9fe97ec47f3c4d490a841212b
Reviewed-on: https://chromium-review.googlesource.com/c/1350615Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610829}

third_party/blink/web_tests/TestExpectations

@@ -5563,5 +5563,5 @@ crbug.com/906320 [ Mac10.13 ] virtual/site-isolated-code-cache/http/tests/devtoo
 
 # Sheriff 2018-11-26
 crbug.com/908276 [ Mac ] external/wpt/webstorage/storage_setitem.html [ Pass Timeout ]
-crbug.com/908347 [ Mac ] external/wpt/event-timing/event-timing-timingconditions.html [ Failure Pass ]
+crbug.com/908347 [ Mac ] media/autoplay/webaudio-audio-context-resume.html [ Failure Pass ]