webui: remove FocusManager.disableMouseFocusOnButtons().

webui: remove FocusManager.disableMouseFocusOnButtons().

It seems to be unnecessary now (tested against bugs: 256127, 256124) and
messes with focus order (i.e. click on a <button>, press tab -> should
go to next focusable item on the page but instead starts at top).

In general I'd also just like to match the rest of the web if possible.

R=tkent@chromium.org
BUG=none
TEST=manual

Committed: https://crrev.com/68673f7785ea1f48017b1d13c74aa80702332c88
Cr-Commit-Position: refs/heads/master@{#315251}

[tkent, 2015-02-08 23:53:22]

lgtm.

Let's try this.

[Dan Beam, 2015-02-09 00:37:33]

The CQ bit was checked by dbeam@chromium.org

[commit-bot: I haz the power, 2015-02-09 00:37:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/905433003/1

[commit-bot: I haz the power, 2015-02-09 00:41:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-09 00:41:31]

Patchset 1 (id:??) landed as
https://crrev.com/68673f7785ea1f48017b1d13c74aa80702332c88
Cr-Commit-Position: refs/heads/master@{#315251}