ShellTest.InitializeWithMultipleThreadButCallingThreadAsPlatformThread is flaky #64906
Description
Saw the following flake on the Mac Host Engine build presubmit on 2020-08-30 at ~11:20am PDT. Re-run passed.
[----------] 54 tests from ShellTest
[ RUN ] ShellTest.InitializeWithMultipleThreadButCallingThreadAsPlatformThread
[ OK ] ShellTest.InitializeWithMultipleThreadButCallingThreadAsPlatformThread (60 ms)
...
[ RUN ] ShellTest.OnPlatformViewDestroyDisablesThreadMerger
../../flutter/shell/common/shell_unittests.cc:89: Failure
Value of: RasterizerHasLayerTree(shell)
Actual: false
Expected: true
[ FAILED ] ShellTest.OnPlatformViewDestroyDisablesThreadMerger (58 ms)