Add SkPathPriv::IsSimpleClosedRect

This function looks for "simple" rect paths. Simple here means begins and ends at a corner and is closed (either manually or with a close verb). Unlike SkPath::isRect this returns the starting point index (using the same start indexing scheme as SkPath::addRect).

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2017313002

Review-Url: https://codereview.chromium.org/2017313002
3 files changed