Add a container window to host the desktop window hierarchy in AURA.

Add a container window to host the desktop window hierarchy in AURA.

This ensures that ZOrder changes within this hierarchy don't affect the ZOrder of windows like tooltips
which are direct children of the root.

This change fixes the issue with the tooltips getting hidden behind the browser window during a tab drag drop
operation.

Reverted the earlier fix in tooltip_controller.cc which destroyed the tooltip when the mouse left the window
bounds. While that works this appears to be a cleaner fix based on a discussion with sky.

I disabled the PopupBlockerBrowserTest.WindowFeatures test on linux aura as it fails for some reason
with this change. Logged a bug to track that https://code.google.com/p/chromium/issues/detail?id=295299

BUG=292530
R=ben@chromium.org
TBR=sky
TEST=Covered by new views unittest TooltipAtTopOfZOrderAfterActivation

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=224544

[ananta, 2013-09-19 18:13:26]

On 2013/09/19 17:36:34, ananta wrote:

Thinking about a good test for this. Will probably be a new CL for that.

[ananta, 2013-09-19 19:00:48]

On 2013/09/19 18:13:26, ananta wrote:
> On 2013/09/19 17:36:34, ananta wrote:
> 
> Thinking about a good test for this. Will probably be a new CL for that.

Added a views unittest TooltipAtTopOfZOrderAfterActivation for this.

[sky, 2013-09-19 20:46:37]

I'm going to redirect this to Ben. I'm not sure if we ever try to focus any
descendants.

[Ben Goodger (Google), 2013-09-19 21:19:18]

lgtm

[ananta, 2013-09-21 01:46:35]

Committed patchset #6 manually as r224544 (presubmit successful).