GitLab

A fairly small roll, not much in it.
* Bump version from 3.7.0 to 3.8.0
* sdefresne's change to the plugin to emit warnings in files that have
  Developer in the path (system headers should still not warn by virtue of
  being system headers; clang doesn't emit warnings in system headers)

BUG=510886

Review URL: https://codereview.chromium.org/1238353002

Cr-Commit-Position: refs/heads/master@{#339838}