Fix for out-of-bounds intersection (found by fuzzer).

Fix for out-of-bounds intersection (found by fuzzer).

Sometimes, the intersection returned by check_intersection() is
out-of-bounds for both edges (above both tops or below both bottoms)
due to floating-point inaccuracy. This causes split_edge() to create a
tiny negative-length edge on one side (which would then assert).
Although we could safely remove this assert and allow the negative
length edge to be removed, it's faster/safer to simply avoid its
creation in the first place by adjusting one edge to the other edge's
endpoint.

Added a new unit test to exercise this case.

Committed: https://skia.googlesource.com/skia/+/a2b6d28755916cbb4817cd9d1cd1b0e237de9a50

[Stephen White, 2015-03-02 16:50:04]

senorblanco@chromium.org changed reviewers:
+ egdaniel@chromium.org

[Stephen White, 2015-03-02 16:50:14]

Greg: PTAL. Thanks!

[egdaniel, 2015-03-02 16:58:40]

egdaniel@google.com changed reviewers:
+ egdaniel@google.com

[egdaniel, 2015-03-02 16:58:40]

lgtm

[Stephen White, 2015-03-02 17:26:57]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2015-03-02 17:28:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/968993002/1

[commit-bot: I haz the power, 2015-03-02 17:34:17]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/a2b6d28755916cbb4817cd9d1cd1b0e237de9a50