Fix self._skp_dir in BuildStep
Fix self._skp_dir in BuildStep

Enables https://codereview.chromium.org/12576012/
(SkipBuildbotRuns)
Review URL: https://codereview.chromium.org/12778006

git-svn-id: 32fc27f4dcfb6c0385cd9719852b95fe6680452d@8145 2bbb7eff-a529-9590-31e7-b0007b416f81

Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot