Add ScopedObjCClassSwizzler in base/mac, absorbs objc_method_swizzle and ScopedClassSwizzler

chrome/common/mac/objc_method_swizzle.mm

-// Copyright (c) 2011 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/common/mac/objc_method_swizzle.h"
-
-#import "base/logging.h"
-
-namespace ObjcEvilDoers {
-
-Method GetImplementedInstanceMethod(Class aClass, SEL aSelector) {
-  Method method = NULL;
-  unsigned int methodCount = 0;
-  Method* methodList = class_copyMethodList(aClass, &methodCount);
-  if (methodList) {
-    for (unsigned int i = 0; i < methodCount; ++i) {
-      if (method_getName(methodList[i]) == aSelector) {
-        method = methodList[i];
-        break;
-      }
-    }
-    free(methodList);
-  }
-  return method;
-}
-
-IMP SwizzleImplementedInstanceMethods(
-    Class aClass, const SEL originalSelector, const SEL alternateSelector) {
-  // The methods must both be implemented by the target class, not
-  // inherited from a superclass.
-  Method original = GetImplementedInstanceMethod(aClass, originalSelector);
-  Method alternate = GetImplementedInstanceMethod(aClass, alternateSelector);
-  DCHECK(original);
-  DCHECK(alternate);
-  if (!original || !alternate) {
-    return NULL;
-  }
-
-  // The argument and return types must match exactly.
-  const char* originalTypes = method_getTypeEncoding(original);
-  const char* alternateTypes = method_getTypeEncoding(alternate);
-  DCHECK(originalTypes);
-  DCHECK(alternateTypes);
-  DCHECK(0 == strcmp(originalTypes, alternateTypes));
-  if (!originalTypes || !alternateTypes ||
-      strcmp(originalTypes, alternateTypes)) {
-    return NULL;
-  }
-
-  IMP ret = method_getImplementation(original);
-  if (ret) {
-    method_exchangeImplementations(original, alternate);
-  }
-  return ret;
-}
-
-}  // namespace ObjcEvilDoers