Fix SchedulerLock unittests to actually generate a DCHECK, not an exception
in SafeAcquisitionTracker::AssertSafePredecessor().

Issue was found when writing https://codereview.chromium.org/2213933003/

BUG=553459
NO_DEPENDENCY_CHECKS=true

Review-Url: https://codereview.chromium.org/2218443002
Cr-Commit-Position: refs/heads/master@{#409879}
1 file changed