Add ScopedObjCClassSwizzler in base/mac, absorbs objc_method_swizzle and ScopedClassSwizzler

base/mac/scoped_objc_class_swizzler.h

+// 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.
+
+#ifndef BASE_MAC_SCOPED_OBJC_CLASS_SWIZZLER_H_
+#define BASE_MAC_SCOPED_OBJC_CLASS_SWIZZLER_H_
+
+#import <objc/runtime.h>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+
+namespace base {
+namespace mac {
+
+// Within a given scope, swaps method implementations of a class interface, or
+// between two class interfaces. The argument and return types must match.
+class BASE_EXPORT ScopedObjCClassSwizzler {
+ public:
+  // Given two classes that each respond to |selector|, swap the implementations
+  // of those methods.
+  ScopedObjCClassSwizzler(Class target, Class source, SEL selector);
+
+  // Given two selectors on the same class interface, |target| (e.g. via
+  // inheritance or categories), swap the implementations of methods |original|
+  // and |alternate|.
+  ScopedObjCClassSwizzler(Class target, SEL original, SEL alternate);
+
+  ~ScopedObjCClassSwizzler();
+
+  // Return a callable function pointer for the replaced method. To call this
+  // from the replacing function, the first two arguments should be |self| and
+  // |_cmd|. These are followed by the (variadic) method arguments.
+  IMP GetOriginalImplementation();
+
+ private:
+  // Delegated constructor.
+  void Init(Class target, Class source, SEL original, SEL alternate);
+
+  Method old_selector_impl_;
+  Method new_selector_impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedObjCClassSwizzler);
+};
+
+}  // namespace mac
+}  // namespace base
+
+#endif  // BASE_MAC_SCOPED_OBJC_CLASS_SWIZZLER_H_