Disable WebMediaPlayerMSTest.CreateHardwareFrames on Fushsia

Flaky.

TBR=scottmg@chromium.org

Bug: 819924
Change-Id: Id6a337392ec94bbc1b3ae2f83a914bc4d2565996
Reviewed-on: https://chromium-review.googlesource.com/958666Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542722}

testing/buildbot/filters/fuchsia.content_unittests.filter

@@ -30,6 +30,9 @@
 -MediaStreamManagerTest.MakeMediaAccessRequest
 -MediaStreamManagerTest.MakeMultipleRequests
 
+# Flaky: http://crbug.com/819924.
+-WebMediaPlayerMSTest.CreateHardwareFrames
+
 # Failing: https://crbug.com/771701.
 -IndexedDBFactoryTest.DataFormatVersion