Revert of fix zero-length tangent

Revert of fix zero-length tangent (patchset #2 id:20001 of https://codereview.chromium.org/1311273002/ )

Reason for revert:
causes layout test to draw differently -- new drawing is more correct. Reverting until layout test ignore is landed.

Original issue's description:
> fix zero-length tangent
> 
> If the end point and the control point are the same, computing
> the tangent will result in (0, 0). In this case, use the prior
> control point instead.
> 
> R=reed@google.com
> 
> BUG=skia:4191
> 
> Committed: https://skia.googlesource.com/skia/+/7544124fb8ee744f68f549a353f8a9163cd7432d

TBR=reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4191
Committed: https://skia.googlesource.com/skia/+/91298b47c547b2ab4697038c04685af957bd1416

[caryclark, 2015-08-25 17:02:33]

Created Revert of fix zero-length tangent

[commit-bot: I haz the power, 2015-08-25 17:02:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1312243002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1312243002/1

[commit-bot: I haz the power, 2015-08-25 17:02:48]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/91298b47c547b2ab4697038c04685af957bd1416

[caryclark, 2015-08-25 20:18:52]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1320473002/ by caryclark@google.com.

The reason for reverting is: Layout suppression has landed, and verified that
Skia gm test changes are correct..