Remove all the OS X 10.6 SDK forward declarations.

base/mac/mac_util.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.
 
 #include "base/mac/mac_util.h"
 
 #import <Cocoa/Cocoa.h>
 #import <IOKit/IOKitLib.h>
 #include <string.h>
 #include <sys/utsname.h>
@@ skipping 77 matching lines @@
       if (CFEqual(item_url, url)) {
         CFRetain(item);
         return item;
       }
     }
   }
 
   return NULL;
 }
 
-#if !defined(MAC_OS_X_VERSION_10_6) || \
-    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_6
-// kLSSharedFileListLoginItemHidden is supported on
-// 10.5, but missing from the 10.5 headers.
-// http://openradar.appspot.com/6482251
-static NSString* kLSSharedFileListLoginItemHidden =
-    @"com.apple.loginitem.HideOnLaunch";
-#endif
-
 bool IsHiddenLoginItem(LSSharedFileListItemRef item) {
   ScopedCFTypeRef<CFBooleanRef> hidden(reinterpret_cast<CFBooleanRef>(
       LSSharedFileListItemCopyProperty(item,
           reinterpret_cast<CFStringRef>(kLSSharedFileListLoginItemHidden))));
 
   return hidden && hidden == kCFBooleanTrue;
 }
 
 }  // namespace
 
@@ skipping 574 matching lines @@
           StringPiece(begin + comma_loc + 1, ident.end()), &minor_tmp))
     return false;
   *type = ident.substr(0, number_loc);
   *major = major_tmp;
   *minor = minor_tmp;
   return true;
 }
 
 }  // namespace mac
 }  // namespace base