Revert of Reland "mac: Layer back the root view of the browser window on OSX 10.9+."

Revert of Reland "mac: Layer back the root view of the browser window on OSX 10.9+." (patchset #1 id:1 of https://codereview.chromium.org/878673006/)

Reason for revert:
Chrome Mac lost its rounded bottom corners
https://code.google.com/p/chromium/issues/detail?id=452707

Original issue's description:
> Reland "mac: Layer back the root view of the browser window on OSX 10.9+."
>
> The original CL was reverted because it caused non-deterministic failures in
> browser tests that used the file tab-restore-visibility.html. The test file had
> an edge case that caused thrashing and prevented the page from loading. This
> has since been fixed.
>
> > BrowserWindowController always layer-backs the contentView of the window. If
> > Chrome were linked against OSX 10.9, this would also cause the root view to be
> > layer backed. Since Chrome is linked against OSX 10.6, the root view by default
> > is not layer backed.
> >
> > BrowserWindowController is going to have a custom AppKit fullscreen animation,
> > which requires that the root view is layer backed. While it is possible to
> > implement a custom AppKit fullscreen animation as early as OSX 10.7, the
> > effects of layer backing the root view on OSX 10.7 are murky. It seems much
> > safer to just layer back the root view on OSX 10.9+, and only enable the custom
> > AppKit fullscreen animation on OSX 10.9+.
> >
> > As far as I know, this change has no detrimental side effects. There is no
> > spike in memory usage
> > (https://code.google.com/p/chromium/issues/detail?id=396264#c11), presumably
> > because NSThemeFrame implements -wantsUpdateLayer on OSX 10.9+.
> >
> > BUG=413009, 414527
> > Committed: https://crrev.com/8dec34f8f3504352e4eef95b2aaa36c561aea930
> > Cr-Commit-Position: refs/heads/master@{#311191}
>
> BUG=413009, 414527
> TBR=rsesek@chromium.org
>
> Committed: https://crrev.com/4713180802457f8c6854c10db4689ab4fab98155
> Cr-Commit-Position: refs/heads/master@{#313207}

TBR=
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=413009, 414527
Committed: https://crrev.com/86b7486d902f7e1389f8a3dad9ff42ee68134076
Cr-Commit-Position: refs/heads/master@{#313401}

[erikchen, 2015-01-27 23:35:42]

Created Revert of Reland "mac: Layer back the root view of the browser window on
OSX 10.9+."

[commit-bot: I haz the power, 2015-01-27 23:36:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/881133002/1

[commit-bot: I haz the power, 2015-01-27 23:38:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-27 23:40:14]

Patchset 1 (id:??) landed as
https://crrev.com/86b7486d902f7e1389f8a3dad9ff42ee68134076
Cr-Commit-Position: refs/heads/master@{#313401}