[OSX] ConstrainedWindow with "proper" background color.

ConstrainedWindow with "proper" background color.

ConstrainedWindow used to have clearColor as backgroundColor - which
means all underlying views had to assume that the background color
was chrome_style::GetBackgroundColor instead of just querying the
window.

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202645

[groby-ooo-7-16, 2013-05-25 03:01:51]

Hi Sailesh!

Per our e-mail thread on background color, this would be an alternative version
of ConstrainedWindowCustomWindow that actually reflects its background color in
the backgroundColor property.

It does that via manually forcing a transparent background in the draw call, 

The second patchset instead lets Cocoa handle the background of the dialog via
backgroundColor, and only draws the transparent "ears" that make it seem round.
It's less brute force, but possibly harder to read.

Worth landing either?

[sail, 2013-05-25 13:05:11]

lgtm

[commit-bot: I haz the power, 2013-05-28 18:18:08]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/groby@chromium.org/15729008/2001

[commit-bot: I haz the power, 2013-05-28 18:49:43]

Step "update" is always a major failure.
Look at the try server FAQ for more details.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2013-05-28 19:10:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/groby@chromium.org/15729008/2001

[commit-bot: I haz the power, 2013-05-28 20:39:34]

Change committed as 202645