Disable a test under fuschia

IndexedDBDispatcherHostTest.NotifyIndexedDBContentChanged is flaky.

TBR=dmurph@chromium.org

Bug: 879213
Change-Id: I933e46c2ec3df71920a1f7f809b80c300f19f80c
Reviewed-on: https://chromium-review.googlesource.com/1246823Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594422}

testing/buildbot/filters/fuchsia.content_unittests.filter

@@ -34,6 +34,9 @@
 -MediaStreamManagerTest.MakeMediaAccessRequest
 -MediaStreamManagerTest.MakeMultipleRequests
 
+# Flaky: https://crbug.com/879213
+-IndexedDBDispatcherHostTest.NotifyIndexedDBContentChanged
+
 # Failing: https://crbug.com/771701.
 -IndexedDBFactoryTest.DataFormatVersion