GitLab

This also adds unittests for ServerLogEntry client code, with common code
pulled out to a separate file.

This doesn't affect LogToServer classes - they will be refactored in a
separate CL. Also fix some IWYU issues uncovered by the refactor.

TEST=unittests

Review URL: https://codereview.chromium.org/282063005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272346 0039d316-1c4b-4281-b951-d872f2087c98