Migrate WaitableEvent to enum-based constructor in thread_watcher_unittest.cc

And fix presubmit checks about usage of static strings.

(and also get rid of constant for thread ID constants..)

BUG=612843
NO_DEPENDENCY_CHECKS=true
TBR=rkaplow@chromium.org (to bypass incorrect owner presubmit inherited from dependency)

Review-Url: https://codereview.chromium.org/2034713002
Cr-Commit-Position: refs/heads/master@{#397414}
1 file changed