base::Thread will store its |name| as a string, so take the name as a string
instead of a char*.

Avoids a bunch of pointless c_str()s on the caller sides.

BUG=none
TEST=none
R=darin@chromium.org

Review URL: https://codereview.chromium.org/243863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@264886 0039d316-1c4b-4281-b951-d872f2087c98