Remove the extension dialog extra border.

Remove the extension dialog extra border.

ExtensionDialog uses Widget::CreateWindowWithParent.
Use DialogDelegate::CreateDialogWidget instead. 
Does not change the old-style appearance or behavior. 
See before/after pics at http://crbug.com/166075#c63 
Trigger the only user (select file dialog extension) in CrOS with CTRL+O.

Also, remove the unused fullscreen dialog codepath.
(Rahul said this is no longer used and may be removed)

BUG=166075
TEST=new-style select file extension dialog does not have an extra border. 
R=sky@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=199646

[msw, 2013-05-10 21:37:39]

Hey Scott, please take a look; thanks!

[sky, 2013-05-10 23:13:04]

LGTM

[commit-bot: I haz the power, 2013-05-10 23:18:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/msw@chromium.org/14830005/2001

[commit-bot: I haz the power, 2013-05-11 07:29:33]

Retried try job too often on win_rel for step(s) interactive_ui_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[commit-bot: I haz the power, 2013-05-11 18:03:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/msw@chromium.org/14830005/2001

[commit-bot: I haz the power, 2013-05-12 22:28:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/msw@chromium.org/14830005/2001

[commit-bot: I haz the power, 2013-05-13 04:01:03]

Change committed as 199646