Some small cleanups for image filter code.

Use the 2-param flavour of mapVector instead of the 3-param, where possible.
Add an SkMatrixImageFilter test case to the tiling unit test.

R=junov@chromium.org

Review URL: https://codereview.chromium.org/277543002

git-svn-id: http://skia.googlecode.com/svn/trunk@14630 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed