Tweaks in how to apply bitmap filter levels in GPU.

Fix fallback to MIP from bicubic for bitmap shaders
Skip MIP level generation on GPU when not minifying
Add medium quality and mixed up/down matrix test cases to filterbitmap tests

R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/103913012

git-svn-id: http://skia.googlecode.com/svn/trunk@12697 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed