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

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

Review URL: https://codereview.chromium.org/881133002

Cr-Commit-Position: refs/heads/master@{#313401}

chrome/browser/ui/cocoa/browser_window_controller.mm

@@ -255,10 +255,7 @@ using content::WebContents;
     // Make the content view for the window have a layer. This will make all
     // sub-views have layers. This is necessary to ensure correct layer
     // ordering of all child views and their layers.
-    if ([self wantsRootViewToBeLayerBacked])
-      [[[window contentView] superview] setWantsLayer:YES];
-    else
-      [[window contentView] setWantsLayer:YES];
+    [[window contentView] setWantsLayer:YES];
     windowShim_.reset(new BrowserWindowCocoa(browser, self));
 
     // Set different minimum sizes on tabbed windows vs non-tabbed, e.g. popups.

chrome/browser/ui/cocoa/browser_window_controller_private.h

@@ -159,9 +159,6 @@
 // out of AppKit Fullscreen.
 - (BOOL)shouldUseCustomAppKitFullscreenTransition;
 
-// Whether the root view of the window should be layer backed.
-- (BOOL)wantsRootViewToBeLayerBacked;
-
 @end  // @interface BrowserWindowController(Private)
 
 #endif  // CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_CONTROLLER_PRIVATE_H_

chrome/browser/ui/cocoa/browser_window_controller_private.mm

@@ -1072,16 +1072,4 @@ willPositionSheet:(NSWindow*)sheet
   return [super shouldConstrainFrameRect];
 }
 
-- (BOOL)wantsRootViewToBeLayerBacked {
-  // This class 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.
-
-  // This class is going to have a custom AppKit fullscreen animation, which
-  // requires that the root view is layer backed. To be safe, this class will
-  // only layer-back the root view on OSX 10.9+.
-  return base::mac::IsOSMavericksOrLater();
-}
-
 @end  // @implementation BrowserWindowController(Private)