Edges matter, part 2.

Edges matter, part 2.

Affected modes: lighten, hard-light, overlay (== hard-light).
This fixes a couple places where I used < when I should have used <=,
or swapped the logic as I've done here.


Caught by layout tests; our tests should be unchanged.
https://storage.googleapis.com/chromium-layout-test-archives/linux_blink_rel/68935/layout-test-results/css3/blending/background-blend-mode-crossfade-image-gradient-diffs.html


BUG=skia:

Committed: https://skia.googlesource.com/skia/+/b743c6679abeeeab998a1147fd6aefd3b4d1fcd9

[mtklein, 2015-06-29 18:54:09]

The CQ bit was checked by mtklein@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-06-29 18:54:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1217013003/1

[mtklein_C, 2015-06-29 18:55:29]

mtklein@chromium.org changed reviewers:
+ reed@google.com
- mtklein@google.com

[reed1, 2015-06-29 19:02:03]

lgtm

[commit-bot: I haz the power, 2015-06-29 19:02:53]

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

[commit-bot: I haz the power, 2015-06-29 19:02:54]

Dry run: This issue passed the CQ dry run.

[mtklein, 2015-06-29 19:03:19]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-06-29 19:03:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1217013003/1

[commit-bot: I haz the power, 2015-06-29 19:04:14]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/b743c6679abeeeab998a1147fd6aefd3b4d1fcd9