reapply r3259 (that was reverted) with fix.

The SkASSERT was incorrect and failing on debug runs.
Review URL: https://codereview.appspot.com/5699071

git-svn-id: http://skia.googlecode.com/svn/trunk@3263 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed