RuntimeTimerScopes always subtract their own time from the parent timer's
counter to properly account for the own time. Once a scope is destructed it
adds it own timer to the current active counter. However, if the current
counter is changed with CorrectCurrentCounterId we will attribute all the
subtimers to the previous counter, and add the own time to the new counter.
This way it is possible to end up with negative times in certain counters but
the overall would still be correct.

BUG=

Review-Url: https://codereview.chromium.org/2511093002
Cr-Commit-Position: refs/heads/master@{#41142}