autofill: Convert AutofillInteractiveTest to use InfoBarManager::Observer.

autofill: Convert AutofillInteractiveTest to use InfoBarManager::Observer.

We are removing notifications (NotificationService API) from InfoBar
code. And thus we need to migrate its uses to the Observer style.
This is what this patch does.

BUG=354380
TEST=browser_tests --gtest_filter=AutofillInteractiveTest.*
R=isherman@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=267958

[Ilya Sherman, 2014-05-02 04:07:52]

LGTM.  Thanks, Thiago.

[tfarina, 2014-05-02 21:16:21]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2014-05-02 21:17:42]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tfarina@chromium.org/269543010/1

[commit-bot: I haz the power, 2014-05-02 22:29:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-05-02 22:29:42]

Try jobs failed on following builders:
  linux_chromium_rel on tryserver.chromium

[tfarina, 2014-05-02 22:33:40]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2014-05-02 22:34:26]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tfarina@chromium.org/269543010/1

[commit-bot: I haz the power, 2014-05-02 23:20:07]

Change committed as 267958