Broaden test filter for TaskSchedulerWorkerPoolHistogramTests.

These tests rely on thread sleeps for synchronization, which makes them
racey when run on heavily-loaded systems.

TBR: scottmg
Bug: 816170, 735701
Change-Id: I9cad471cf8bc88fd91dc33662489983f13f18786
Reviewed-on: https://chromium-review.googlesource.com/936446Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539025}

testing/buildbot/filters/fuchsia.base_unittests.filter

@@ -82,8 +82,8 @@
 # Flaky, https://crbug.com/810077.
 -MessageLoopTypedTest.RecursivePosts/*
 
-# Flaky, https://crbug.com/735701.
--TaskSchedulerWorkerPoolHistogramTest.NumTasksBeforeCleanup
+# Flaky, https://crbug.com/735701 and https://crbug.com/816170.
+-TaskSchedulerWorkerPoolHistogramTest.NumTasks*Cleanup
 
 # Flaky, https://crbug.com/811881
 -AddressSpaceRandomizationTest.RandomBitCorrelations*