add SkPath::isRRect

Add helper to track when a round rect was added to a path,
and then return the SkRRect specification that describes it.

Move the implementation for SkPath::RawIter to SkPathRef so it can be used there as well.

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

Review URL: https://codereview.chromium.org/1461763004
5 files changed