Base: Make RegistryOverrideManager support sharded/parallel tests.

BUG=314800
TBR=ajwong@chromium.org

Review URL: https://codereview.chromium.org/57423008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234367 0039d316-1c4b-4281-b951-d872f2087c98
Fix trace-startup filtering

BUG=314918
R=piman

Review URL: https://codereview.chromium.org/66393005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234368 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234368