Prevent overflow by falling back to non-AA

Prevent overflow by falling back to non-AA

This piece of code is directly copied from our old supersampling AA
code. I didn not preserve this code because it's not triggered by any Skia
tests. However, this will be critical to Chromium's tests as some
websites will generate huge paths!

I'm not so sure whether the long_running_idle_gmail_background_tbmv2 test
failed because of this. But I'm sure that www.nationalgeographic.com from
page_cycler_v2.typical_25 failed because of this.

BUG=chromium:660394

TBR=reed@google.com,caryclark@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2461133002

Review-Url: https://codereview.chromium.org/2461133002