Aura/Ash split: Move ScreenAura to ash::ScreenAsh.

Aura/Ash split: Move ScreenAura to aura::RootWindowScreen.

What is now aura::RootWindowScreen was tightly bundled with aura::RootWindow. Instead of moving it to ash::ScreenAsh, I renamed it aurea::RootWindowScreen because there's a bunch of unit tests that use RootWindow as if it were the desktop. Screen integration stuff has been moved out of RootWindow (and related observers) and into ash::Shell.

BUG=116458
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=125950

[Elliot Glaysher, 2012-03-09 00:09:19]

ptal.

Something will have to be done about the ui side of Screen, but not in this
patch.

[Ben Goodger (Google), 2012-03-09 21:06:11]

lgtm

[commit-bot: I haz the power, 2012-03-09 21:13:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/erg@chromium.org/9616045/20001

[commit-bot: I haz the power, 2012-03-09 21:54:17]

Try job failure for 9616045-20001 (retry) on linux_clang for step "compile"
(clobber build).
It's a second try, previously, step "compile" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_clan...

[commit-bot: I haz the power, 2012-03-09 22:05:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/erg@chromium.org/9616045/20001

[commit-bot: I haz the power, 2012-03-10 00:18:51]

Change committed as 125950