git-svn-id: http://skia.googlecode.com/svn/trunk@827 2bbb7eff-a529-9590-31e7-b0007b416f81
for another iter that runs back-to-front (B2FIter). add unittest for Deque git-svn-id: http://skia.googlecode.com/svn/trunk@821 2bbb7eff-a529-9590-31e7-b0007b416f81