Changed the render_pictures, bench_pictures and test_pictures.py so that multiple inputs can be given. Furthermore, specific files can also be specified.
Unit tests have also been added for picture_utils.cpp.
Review URL: https://codereview.appspot.com/6345054
git-svn-id: http://skia.googlecode.com/svn/trunk@4486 2bbb7eff-a529-9590-31e7-b0007b416f81