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

chrome/browser/ui/cocoa/browser_window_controller_private.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "chrome/browser/ui/cocoa/browser_window_controller_private.h"
 
 #include <cmath>
 
 #include "base/command_line.h"
 #include "base/mac/bind_objc_block.h"
@@ skipping 1054 matching lines @@
       startCustomAnimationToEnterFullScreenWithDuration:duration];
 }
 
 - (BOOL)shouldConstrainFrameRect {
   if ([enterFullscreenTransition_ shouldWindowBeUnconstrained])
     return NO;
 
   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)