mac: Fix tab dragging visual bug in Yosemite. (reland 2)

chrome/browser/ui/cocoa/fullscreen_window.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/fullscreen_window.h"
 
+#import "chrome/browser/ui/cocoa/nsview_additions.h"
 #import "chrome/browser/ui/cocoa/themed_window.h"
 
 @implementation FullscreenWindow
 
 // Make sure our designated initializer gets called.
 - (id)init {
   return [self initForScreen:[NSScreen mainScreen]];
 }
 
 - (id)initForScreen:(NSScreen*)screen {
   NSRect contentRect;
   contentRect.origin = NSZeroPoint;
   contentRect.size = [screen frame].size;
 
   if ((self = [super initWithContentRect:contentRect
                                styleMask:NSBorderlessWindowMask
                                  backing:NSBackingStoreBuffered
                                    defer:YES
                                   screen:screen])) {
     [self setReleasedWhenClosed:NO];
     // Borderless windows don't usually show up in the Windows menu so whine at
     // Cocoa until it complies. See -dealloc and -setTitle: as well.
     [NSApp addWindowsItem:self title:@"" filename:NO];
+    [[self contentView] cr_setWantsLayer:YES];
   }
   return self;
 }
 
 - (void)dealloc {
   // Paranoia; doesn't seem to be necessary but it doesn't hurt.
   [NSApp removeWindowsItem:self];
 
   [super dealloc];
 }
@@ skipping 49 matching lines @@
 
   // Explicitly enable |-performClose:| (see above); otherwise the fact that
   // this window does not have a close button results in it being disabled.
   if (action == @selector(performClose:))
     return YES;
 
   return [super validateUserInterfaceItem:item];
 }
 
 @end