GTTF: Disable new test launcher under Valgrind.

Currently it breaks sanity tests.

BUG=236893
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/107153003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239045 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239045