add rounding-using-doubles methods on SkScalar and SkRect

Inspired by the excellent repro case for https://crbug.com/364224

patch from issue 265933010

BUG=skia:
R=bungeman@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/267003002

git-svn-id: http://skia.googlecode.com/svn/trunk/include@14566 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed