Add function to get both min and max scale factors from matrix

R=reed@google.com, jvanverth@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/298473002

git-svn-id: http://skia.googlecode.com/svn/trunk@14804 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed