Remove NSWindowHostsLayersInWindowServer workaround.

content/app/mac/mac_init.mm

 // Copyright 2015 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.
 
 #include "content/app/mac/mac_init.h"
 
 #import <Cocoa/Cocoa.h>
 
 namespace content {
 
 void InitializeMac() {
   [[NSUserDefaults standardUserDefaults] registerDefaults:@{
       // Exceptions routed to -[NSApplication reportException:] should crash
       // immediately, as opposed being swallowed or presenting UI that gives the
       // user a choice in the matter.
       @"NSApplicationCrashOnExceptions": @YES,
 
       // Prevent Cocoa from turning command-line arguments into -[NSApplication
       // application:openFile:], because they are handled directly. @"NO" looks
       // like a mistake, but the value really is supposed to be a string.
       @"NSTreatUnknownArgumentsAsOpen": @"NO",
-
-      // CoreAnimation has poor performance and CoreAnimation and
-      // non-CoreAnimation exhibit window flickering when layers are not hosted
-      // in the window server, which is the default when not not using the
-      // 10.9 SDK.
-      // TODO: Remove this when we build with the 10.9 SDK.
-      @"NSWindowHostsLayersInWindowServer": @YES
   }];
 }
 
 }  // namespace content