[Fuchsia] Filter slow SimpleURLLoaderTest.OnUploadProgressCallback case.

This test flakes frequently under Fuchsia, due to its run-time being
too close to the per-test timeout, and varying sufficiently that it
sometimes exceeds it.

Bug: 976319
Change-Id: I1bb9e9726511c1a577a827eccebb1c6cd92239d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663907
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671562}

testing/buildbot/filters/fuchsia.services_unittests.filter

@@ -23,3 +23,6 @@
 
 # https://crbug.com/925653 - Unexpected address-in-use.
 -TCPBoundSocketTest.ListenError
+
+# https://crbug.com/976319 - Flakily times-out due to virtualization overhead.
+-SimpleURLLoaderTest.OnUploadProgressCallback/*