Fix logic surrounding window / root window coordinates in Ash.

Fix logic surrounding window / root window coordinates in Ash.

This was causing, among potentially other side effects, javascript
functions window.screenX and window.screenY to always return (0,0)
in Windows Ash.

BUG=318614
TESTS=
 1) Verified correct behavior of window.screenX and window.screenY in both desktop and ash, in regular / maximized state.  
 2) Verified correct behavior of fullscreen flash / HTML5 video.  
 3) Verified no issues arise on Win7 classic mode.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=264072

[zturner, 2014-04-11 01:05:47]

Been continuing to try to break this, and everything appears to work.  My test
matrix includes every combination of {fullscreen, not fullscreen} x {desktop,
metro} x {maximized, not maximized} x {HTML5 video, flash video, no video} x
{classic theme, aero theme}

[Ben Goodger (Google), 2014-04-15 17:44:32]

lgtm

[zturner, 2014-04-15 17:45:20]

The CQ bit was checked by zturner@chromium.org

[commit-bot: I haz the power, 2014-04-15 17:46:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/zturner@chromium.org/231723005/1

[commit-bot: I haz the power, 2014-04-16 01:21:08]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/zturner@chromium.org/231723005/1

[commit-bot: I haz the power, 2014-04-16 02:35:27]

Change committed as 264072