[chromedriver] Remove invalid assertions from tests.

[chromedriver] Remove invalid assertions from tests.

These tests assume that no extension background pages have loaded at the start
of the test, but for some reason DevTools is reporting these earlier than it
used to. It's valid to have these background pages in the window list, so I've
removed the assertions.

BUG=
TBR=stgao@chromium.org

Committed: https://crrev.com/e6877e7e07e21d42dc1fb57184c0ff2851b9e859
Cr-Commit-Position: refs/heads/master@{#415701}

[samuong, 2016-08-31 17:49:41]

The CQ bit was checked by samuong@chromium.org

[commit-bot: I haz the power, 2016-08-31 17:50:26]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[stgao, 2016-08-31 18:04:23]

lgtm

[commit-bot: I haz the power, 2016-08-31 18:50:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-31 18:52:44]

Description was changed from

==========
[chromedriver] Remove invalid assertions from tests.

These tests assume that no extension background pages have loaded at the start
of the test, but for some reason DevTools is reporting these earlier than it
used to. It's valid to have these background pages in the window list, so I've
removed the assertions.

BUG=
TBR=stgao@chromium.org
==========

to

==========
[chromedriver] Remove invalid assertions from tests.

These tests assume that no extension background pages have loaded at the start
of the test, but for some reason DevTools is reporting these earlier than it
used to. It's valid to have these background pages in the window list, so I've
removed the assertions.

BUG=
TBR=stgao@chromium.org

Committed: https://crrev.com/e6877e7e07e21d42dc1fb57184c0ff2851b9e859
Cr-Commit-Position: refs/heads/master@{#415701}
==========

[commit-bot: I haz the power, 2016-08-31 18:52:45]

Patchset 1 (id:??) landed as
https://crrev.com/e6877e7e07e21d42dc1fb57184c0ff2851b9e859
Cr-Commit-Position: refs/heads/master@{#415701}

[samuong, 2016-09-01 16:55:32]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2295403003/ by samuong@chromium.org.

The reason for reverting is: reverting in favor of crrev.com/415873, which fixes
the way we handle background pages from devtools.