credits to gcov.

R=cbruni@chromium.org

Review URL: https://codereview.chromium.org/1522273003

Cr-Commit-Position: refs/heads/master@{#32877}

This is a pure refactor and does not change functionality.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/1264993002

Cr-Commit-Position: refs/heads/master@{#29995}