Filter some Mojo tests that are too slow under QEMU software emulation.

Bug: 780317
Change-Id: I472b726726629139b57b73d7c010d9aa9744052b
Reviewed-on: https://chromium-review.googlesource.com/748202Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513064}

testing/buildbot/filters/fuchsia.mojo_system_unittests.filter

@@ -7,3 +7,7 @@
 # These tests require support for named channels. See crbug.com/754038.
 -MultiprocessMessagePipeTestWithPeerSupport*/2
 -MultiprocessMessagePipeTestWithPeerSupport*/3
+
+# crbug.com/780317 - These timeout under QEMU s/w emulation of ARM64.
+-MultiprocessMessagePipeTestWithPeerSupport.PingPongPipe*
+-MessagePipeTest.SharedBufferHandlePingPong