Clean up SkImageFilter.

Rename more occurences of 'target' to 'kernelOffset'.
This is a follow-up patch to
https://codereview.chromium.org/182983003/

BUG=skia:2187
R=senorblanco@chromium.org

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/197013003

git-svn-id: http://skia.googlecode.com/svn/trunk@13768 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed