Flaky: autoplay/webaudio-audio-context-resume.html

Flaky on all Mac targets. See:

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=media%2Fautoplay%2Fwebaudio-audio-context-resume.html

TBR=mlamouri@chromium.org

Bug: 908347
Change-Id: Ibe20cc3fd8a6cc91569a6b5119472ca8a99bfe8a
Reviewed-on: https://chromium-review.googlesource.com/c/1349979Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610792}

third_party/blink/web_tests/TestExpectations

@@ -5561,4 +5561,5 @@ crbug.com/906320 [ Mac10.13 ] virtual/site-isolated-code-cache/http/tests/devtoo
 
 # Sheriff 2018-11-26
 crbug.com/908276 [ Mac10.10 ] external/wpt/webstorage/storage_setitem.html [ Pass Timeout ]
+crbug.com/908347 [ Mac ] external/wpt/event-timing/event-timing-timingconditions.html [ Failure Pass ]