Add ScopedObjCClassSwizzler in base/mac, absorbs objc_method_swizzle and ScopedClassSwizzler

ui/events/test/cocoa_test_event_utils.mm

 // Copyright 2014 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 <Cocoa/Cocoa.h>
 
 #include "ui/events/test/cocoa_test_event_utils.h"
 
-ScopedClassSwizzler::ScopedClassSwizzler(Class target, Class source,
-                                         SEL selector) {
-  old_selector_impl_ = class_getInstanceMethod(target, selector);
-  new_selector_impl_ = class_getInstanceMethod(source, selector);
-  if (!old_selector_impl_ && !new_selector_impl_) {
-    // Try class methods.
-    old_selector_impl_ = class_getClassMethod(target, selector);
-    new_selector_impl_ = class_getClassMethod(source, selector);
-  }
-  method_exchangeImplementations(old_selector_impl_, new_selector_impl_);
-}
-
-ScopedClassSwizzler::~ScopedClassSwizzler() {
-  method_exchangeImplementations(old_selector_impl_, new_selector_impl_);
-}
-
 namespace cocoa_test_event_utils {
 
 NSEvent* MouseEventAtPoint(NSPoint point, NSEventType type,
                            NSUInteger modifiers) {
   if (type == NSOtherMouseUp) {
     // To synthesize middle clicks we need to create a CGEvent with the
     // "center" button flags so that our resulting NSEvent will have the
     // appropriate buttonNumber field. NSEvent provides no way to create a
     // mouse event with a buttonNumber directly.
     CGPoint location = { point.x, point.y };
@@ skipping 107 matching lines @@
                        modifierFlags:0
                            timestamp:0
                         windowNumber:0
                              context:nil
                              subtype:0
                                data1:0
                                data2:0];
 }
 
 }  // namespace cocoa_test_event_utils