Use stroked rrects for Android shadow sample

Changes the Android shadow sample to use stroked roundrects when
we can (mainly if stroked geometry area < fill geometry area).

Also changes the setup for the overstroke geometry so that it computes
the correct distance to the outer edge.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2283003003

Review-Url: https://codereview.chromium.org/2283003003
3 files changed