[Metro] Focus the user manager's web contents after the widget is shown

[Metro] Focus the user manager's web contents after the widget is shown

Otherwise, on Ash, it seems to steal the initial focus away from the
widget.

BUG=453284
TEST=Start Chrome with --enable-new-avatar menu, and in Metro mode.
Choose "Switch Person" from the avatar menu. In the user manager, start
tabbing (without clicking on the user manager). This should work, and
tabbing should change the selected user pod.

Committed: https://crrev.com/a6afbb6a2348be8e59395c9e6f1ac543fd44f79c
Cr-Commit-Position: refs/heads/master@{#314248}

[noms (inactive), 2015-02-02 23:21:33]

noms@chromium.org changed reviewers:
+ sky@chromium.org

[noms (inactive), 2015-02-02 23:21:33]

I think this focus order makes more sense. Please take a look. Thanks!

[noms (inactive), 2015-02-02 23:21:34]

I think this focus order makes more sense. Please take a look. Thanks!

[sky, 2015-02-03 00:42:16]

LGTM

[noms (inactive), 2015-02-03 02:14:30]

The CQ bit was checked by noms@chromium.org

[commit-bot: I haz the power, 2015-02-03 02:15:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/894723003/1

[commit-bot: I haz the power, 2015-02-03 02:20:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-03 02:21:36]

Patchset 1 (id:??) landed as
https://crrev.com/a6afbb6a2348be8e59395c9e6f1ac543fd44f79c
Cr-Commit-Position: refs/heads/master@{#314248}