Accept displacement with no displacement input

BUG=
R=senorblanco@google.com, senorblanco@chromium.org, sugoi@google.com, bsalomon@google.com, bsalomon@chromium.org

Author: sugoi@chromium.org

Review URL: https://codereview.chromium.org/104853005

git-svn-id: http://skia.googlecode.com/svn/trunk@12773 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed