Working plumb of image scaling:

1) always generate mipmaps if we detect that we are downsampling.
2) pre-scale the image if we detect that we are upsampling
   (currently valid for scale+translate only)
3) A few miscellaneous bug fixes related to image scaling.

Still need SSE/Neon versions of these image scalers.

BUG=
R=bsalomon@google.com, robertphillips@google.com

Review URL: https://codereview.chromium.org/18978014

git-svn-id: http://skia.googlecode.com/svn/trunk@10056 2bbb7eff-a529-9590-31e7-b0007b416f81
17 files changed