Revert of Make ancestors of modal <dialog> inert

Revert of Make ancestors of modal <dialog> inert (https://codereview.chromium.org/133393002/)

Reason for revert:
This patch is the most probable cause of the failing content_browsertests:

AccessibilityModalDialogInIframeOpened
AccessibilityModalDialogOpened
AccessibilityModalDialogStack

See:

http://build.chromium.org/p/chromium.webkit/builders/Win7%20Tests/builds/529

http://build.chromium.org/p/chromium.webkit/builders/Win7%20%28dbg%29/builds/13227

http://build.chromium.org/p/chromium.webkit/builders/Mac10.6%20Tests/builds/22361

http://build.chromium.org/p/chromium.webkit/builders/Mac10.8%20Tests/builds/5388

I could not reach the patch author on IRC due to the time zone difference.

Original issue's description:
> Make ancestors of modal <dialog> inert
> 
> As per spec change: http://html5.org/r/8343
> 
> Now, document.body is also inert. Previously events that
> "skipped" an inert node were fired on document.body; now,
> they are fired on document.
> 
> Test: modal-dialog-ancestor-is-inert.html
> Also, other tests cover some of this behavior and have
> expectations updated.
> 
> BUG=329407
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165040

TBR=esprehn@chromium.org,falken@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=329407
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165086

[tdanderson, 2014-01-14 18:24:31]

Created Revert of Make ancestors of modal <dialog> inert

[commit-bot: I haz the power, 2014-01-14 18:27:13]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdanderson@chromium.org/138183003/1

[commit-bot: I haz the power, 2014-01-14 18:31:49]

Change committed as 165086

[esprehn, 2014-01-14 18:32:19]

lgtm