Update gm self-test to pass again after r6585

Update gm self-test to pass again after r6585
Now depends on only "dashing2" test, not all tests whose name starts with "dashing",
so it should be more resilient in the face of further changes.
TBR=borenet,robertphillips
Committed: https://code.google.com/p/skia/source/detail?r=6588

[EricB, 2012-11-28 20:14:21]

LGTM