Add tests for Chrome Stability Metrics.

BUG=526198,467920

Committed: https://crrev.com/32a86c2579e167dd1e181676056c202f5191852d
Cr-Commit-Position: refs/heads/master@{#346436}

Review URL: https://codereview.chromium.org/1323703002

Cr-Commit-Position: refs/heads/master@{#346956}
5 files changed