cc_unittests hangs forever if run locally on Linux Debug:

Still waiting for the following processes to finish:
	./out/Debug/cc_unittests --gtest_flagfile=/tmp/.org.chromium.Chromium.owAoNW/.org.chromium.Chromium.coLukB --single-process-tests --test-launcher-output=/tmp/.org.chromium.Chromium.OvgnIr/test_results.xml

Flakiness is reduced if you re-run that single batch from the flagfile,
but still able to repro sometimes:

./out/Debug/cc_unittests --gtest_filter=LayerTreeHostTilesTestPartialInvalidation.PartialRaster_MultiThread_OneCopy:LayerTreeHostTilesTestPartialInvalidation.FullRaster_MultiThread_OneCopy:LayerTreeHostTilesTestPartialInvalidation.PartialRaster_SingleThread_Software:LayerTreeHostTilesTestPartialInvalidation.FulllRaster_SingleThread_Software:LayerTreeHostTilesTestPartialInvalidation.PartialRaster_SingleThread_GpuRaster:LayerTreeHostTilesTestPartialInvalidation.FullRaster_SingleThread_GpuRaster:LayerTreeHostTestHasImplThreadTest.RunSingleThread_DelegatingRenderer:LayerTreeHostTestHasImplThreadTest.RunMultiThread_DelegatingRenderer:LayerTreeHostTestSetNeedsCommitInsideLayout.RunSingleThread_DelegatingRenderer:LayerTreeHostTestSetNeedsCommitInsideLayout.RunMultiThread_DelegatingRenderer

It produces:
../../cc/test/layer_tree_pixel_test.cc:101: Failure
Value of: result->HasBitmap()
  Actual: false
Expected: true
... and hangs.

It looks like LayerTreePixelTest::CreateCopyOutputRequest may fail asynchronously and LayerTreePixelTest::EndTest/TryEndTest doesn't solve the problem.