MatchSvnGlob uses the root url to grep for existing svn commits by
matching the git-svn-id lines in the commit messages.  If there is a
rewriteRoot config, then the git-svn-id lines will have the
rewritten url's, and the code should match against that.

R=blundell@chromium.org,maruel@chromium.org

Review URL: https://codereview.chromium.org/103053011

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@241043 0039d316-1c4b-4281-b951-d872f2087c98