fix SkASSERT for Visual Studio

Changing colons to parens permits
the error to be recognized, so that
clicking on it goes to the source
line with the assert.

R=reed@google.com

Change-Id: Ifec7fc0633e8ecf0f670418fefaf8ca87ee3d498
Reviewed-on: https://skia-review.googlesource.com/16485
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Cary Clark <caryclark@skia.org>
1 file changed