Fix scroll-related issues.

Fix scroll-related issues.

This fixes two related issues:
* Scrolling was broken in apps v2, due to window-body div not being
  full-height.
* Scrolling was broken post-disconnect, due to the addition of an explicit
  scroller node, separate from the body.
* The dialog screen was off by 1px, due to the addition of the window-body
  div.

Since this has broken a few times now, I plan to add a browser to test to verify
the behaviour, but I don't want to hold up this CL for that.

BUG=251443
Committed: https://crrev.com/14f7b1a1738a68e55e816dc8f75fb75d0202c514
Cr-Commit-Position: refs/heads/master@{#293431}

[Jamie, 2014-09-04 22:52:44]

jamiewalch@chromium.org changed reviewers:
+ garykac@chromium.org

[garykac1, 2014-09-04 22:58:02]

garykac@google.com changed reviewers:
+ garykac@google.com

[garykac1, 2014-09-04 22:58:02]

lgtm

[Jamie, 2014-09-04 23:01:38]

The CQ bit was checked by jamiewalch@chromium.org

[commit-bot: I haz the power, 2014-09-04 23:02:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jamiewalch@chromium.org/539403002/1

[commit-bot: I haz the power, 2014-09-05 04:10:11]

Committed patchset #1 (id:1) as aa6cd4755ca056d747613b775bd5164bc2facb45

[commit-bot: I haz the power, 2014-09-10 03:36:34]

Patchset 1 (id:??) landed as
https://crrev.com/14f7b1a1738a68e55e816dc8f75fb75d0202c514
Cr-Commit-Position: refs/heads/master@{#293431}