Implement the y-transpose optimization in image (RGBA) blurs.  This gives ~38% performance improvement on my Linux box. Also unify the box blur functions with a template.

R=mtklein@google.com, mtklein, reed@google.com

Review URL: https://codereview.chromium.org/59133006

git-svn-id: http://skia.googlecode.com/svn/trunk/src@12171 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed