fix cubic clip in y

fix cubic clip in y


Follow on to https://codereview.chromium.org/1299243002/

Clip using a geometric solution if the algebraic solution
fails in Y as well as in X.

If the root finder discovers real roots that are sufficiently
far apart, the root in the range of 0..1 can contain so much
error that it is computed to be slightly smaller than 0 or
larger than 1.

In this case, binary search the mono curve for the actual
answer.

R=reed@google.com

Committed: https://skia.googlesource.com/skia/+/05424f77fa8812b6c9e3a21def954e2c8971886a

[caryclark, 2015-08-20 17:18:08]

The CQ bit was checked by caryclark@google.com

[commit-bot: I haz the power, 2015-08-20 17:18:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1303873003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1303873003/1

[commit-bot: I haz the power, 2015-08-20 17:18:27]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-08-20 23:18 UTC

[reed1, 2015-08-20 17:34:44]

lgtm

[commit-bot: I haz the power, 2015-08-20 17:35:46]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/05424f77fa8812b6c9e3a21def954e2c8971886a