Fix password manager subframe test to watch for navigation in subframe.

Fix password manager subframe test to watch for navigation in subframe.

It looks like the intent of this test is to make sure that the password
prompt doesn't show up for a failed login in a subframe. However, the
test is a bit odd: it races the form submit and navigation of the main
frame. Presumably, this was done so NavigationObserver can wait for the
top-level navigation of the page and observer success/failure of the
test conditions. Since NavigationObserver can wait for subframes to
load, just fix the test to wait for the subframe to commit.

BUG=464764
Committed: https://crrev.com/aa719a69b0fade8bd70e31886ac0dbf09cb9f0ce
Cr-Commit-Position: refs/heads/master@{#323951}

[dcheng, 2015-04-04 13:48:48]

dcheng@chromium.org changed reviewers:
+ gcasto@chromium.org

[dcheng, 2015-04-04 13:48:49]

The test JS is a bit odd, since it submits a subframe and navigates the
top-level frame simultaneously. This is racy by nature, and depends on a lot of
implementation details of various things inside Blink. This is currently
blocking a significant cleanup patch from being landed:
https://codereview.chromium.org/1052993006/

[Garrett Casto, 2015-04-06 20:28:40]

lgtm

[dcheng, 2015-04-06 20:32:29]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-04-06 20:32:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1059093003/1

[commit-bot: I haz the power, 2015-04-06 21:10:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-06 21:12:40]

Patchset 1 (id:??) landed as
https://crrev.com/aa719a69b0fade8bd70e31886ac0dbf09cb9f0ce
Cr-Commit-Position: refs/heads/master@{#323951}