Fix debug crash when compositing keyword animations together

Fix debug crash when compositing keyword animations together

This change makes CSSValueInterpolationType composite by replacement
instead of crashing in debug.

Committed: https://crrev.com/e450c785ae3f5937d93b3b305460193fccbcc30d
Cr-Commit-Position: refs/heads/master@{#353940}

[alancutter (OOO until 2018), 2015-10-13 06:52:11]

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

[dstockwell, 2015-10-13 06:54:53]

lgtm

[alancutter (OOO until 2018), 2015-10-13 06:56:47]

The CQ bit was checked by alancutter@chromium.org

[alancutter (OOO until 2018), 2015-10-13 06:56:57]

The CQ bit was unchecked by alancutter@chromium.org

[alancutter (OOO until 2018), 2015-10-14 00:08:54]

The CQ bit was checked by alancutter@chromium.org

[alancutter (OOO until 2018), 2015-10-14 00:08:55]

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/1401853002/#ps20001
(title: "Rebased")

[commit-bot: I haz the power, 2015-10-14 00:11:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1401853002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1401853002/20001

[commit-bot: I haz the power, 2015-10-14 02:14:00]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-14 02:15:36]

Patchset 2 (id:??) landed as
https://crrev.com/e450c785ae3f5937d93b3b305460193fccbcc30d
Cr-Commit-Position: refs/heads/master@{#353940}