GTTF: Replace base::LaunchTests with public TestLauncher class.

This just moves the code around.

BUG=236893
R=sky@chromium.org

Review URL: https://codereview.chromium.org/27630002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229171 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229171