Fix nearly-vertical gradient assert

Fix nearly-vertical gradient assert

Use a SkScalarNearlyZero(dx) test instead of !SkScalarIsFinite(invDx).

R=reed@google.com

Committed: https://skia.googlesource.com/skia/+/8d381022e72f49c2ad02c6fc3fbbb6f03c95bdf2

[f(malita), 2015-11-19 17:59:41]

Passes unit test + problematic Blink layout test.

[f(malita), 2015-11-19 17:59:49]

The CQ bit was checked by fmalita@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-19 17:59:56]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456783005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456783005/1

[commit-bot: I haz the power, 2015-11-19 18:13:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-19 18:13:42]

Dry run: This issue passed the CQ dry run.

[f(malita), 2015-11-19 18:15:35]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2015-11-19 18:15:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456783005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456783005/1

[commit-bot: I haz the power, 2015-11-19 18:15:42]

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 2015-11-20 00:15 UTC

[reed1, 2015-11-19 18:33:02]

lgtm

[commit-bot: I haz the power, 2015-11-19 18:35:36]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/8d381022e72f49c2ad02c6fc3fbbb6f03c95bdf2