rebaseline.py: add ability to write new expectations to a different file
(instead of overwriting the original expectations file)

R=zachr@google.com

Review URL: https://codereview.chromium.org/19805007

git-svn-id: http://skia.googlecode.com/svn/trunk@10333 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed