Stop handling neutral keyframes in CSSValueInterpolationType

Stop handling neutral keyframes in CSSValueInterpolationType

Small clean up patch that makes CSSValueInterpolationType no longer
handle neutral values. This lets certain property specific neutral
keyframes convert as nullptr and skip being applied.

Committed: https://crrev.com/61517d4a243fe1a7cd0b158bc1459e82307be75e
Cr-Commit-Position: refs/heads/master@{#353935}

[alancutter (OOO until 2018), 2015-10-13 06:56:39]

alancutter@chromium.org changed reviewers:
+ dstockwell@chromium.org

[dstockwell, 2015-10-13 07:37:10]

lgtm

[alancutter (OOO until 2018), 2015-10-14 00:08:25]

The CQ bit was checked by alancutter@chromium.org

[alancutter (OOO until 2018), 2015-10-14 00:08:25]

The patchset sent to the CQ was uploaded after l-g-t-m from
dstockwell@chromium.org
Link to the patchset: https://codereview.chromium.org/1401863002/#ps20001
(title: "Rebased")

[commit-bot: I haz the power, 2015-10-14 00:09:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1401863002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1401863002/20001

[commit-bot: I haz the power, 2015-10-14 01:17:31]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-14 01:18:24]

Patchset 2 (id:??) landed as
https://crrev.com/61517d4a243fe1a7cd0b158bc1459e82307be75e
Cr-Commit-Position: refs/heads/master@{#353935}