add extra flag (currently unused) for high quality downsampling

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

Review URL: https://codereview.chromium.org/18386006

git-svn-id: http://skia.googlecode.com/svn/trunk@9927 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed