revised strokerect gm

In service of the bug below, revise the gm to show what zero
widths draw, and what they should draw (by including rects
with fractionally tiny widths).

TBR=halcanary@google.com,reed@google.com
BUG=1294
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1548643002

Review URL: https://codereview.chromium.org/1548643002
1 file changed