... by
1) avoiding accessing RuntimeCallStats instance,
2) avoiding calculating address of a counter field,
3) and using statically known pointer to a member counter instead.

And in addition some code cleanup.

BUG=chromium:596055
LOG=N

Review-Url: https://codereview.chromium.org/1965133002
Cr-Commit-Position: refs/heads/master@{#36162}