This reverts https://codereview.chromium.org/2077613002/.

The check was supposed to tell us whether GPU process main
thread's message pump was signaled at the time of the hang.
In practice 100% of crash dumps had the negative result.
After some additional research I realized that that was
a false negative and that this check doesn't work as
expected with auto-reset events. I confirmed that an
auto-reset event gets promptly reset back to non-signaled
when it gets signaled as long as there is at least one
thread already waiting on it. That is the case even when
when the target thread is never scheduled to run. The
check would work with a manual-reset event but apparently
it is useless in the case of an auto-reset event.

BUG=620904
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2393333002
Cr-Commit-Position: refs/heads/master@{#424040}