Test ThreadTicks.ThreadNow fails on systems with low resolution
thread timers because the tests detects that no time elapsed
since the beginning of the test.
This CL adds a counting loop that makes sure the thread
timer has progressed by at least one tick.

TEST=unittests/ThreadTicks.ThreadNow

Change-Id: I910309208b3a154798cbc43813d41d3755ab819d
Reviewed-on: https://chromium-review.googlesource.com/1082352
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53548}