Calendar Picker: Make month popup cells non-focusable.

Calendar Picker: Make month popup cells non-focusable.

We used <button> for cells, and we had unexpected focus behaviors. This CL
changes <button> to <div>.
This is a preparation to support accessibility in the month popup.

BUG=123896
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181781

[tkent, 2014-09-11 00:48:58]

tkent@chromium.org changed reviewers:
+ keishi@chromium.org

[tkent, 2014-09-11 00:48:59]

Keishi, would you review this please?

[keishi, 2014-09-11 02:08:09]

lgtm

[tkent, 2014-09-11 02:22:32]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2014-09-11 02:22:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/556323003/1

[commit-bot: I haz the power, 2014-09-11 02:26:17]

Committed patchset #1 (id:1) as 181781