[ios] Adds ScopedBlockSwizzler.

ios/chrome/test/base/scoped_block_swizzler.h

Index: ios/chrome/test/base/scoped_block_swizzler.h
diff --git a/ios/chrome/test/base/scoped_block_swizzler.h b/ios/chrome/test/base/scoped_block_swizzler.h
new file mode 100644
index 0000000000000000000000000000000000000000..ecfea71222b64a86939c89a482712749fef2dab2
--- /dev/null
+++ b/ios/chrome/test/base/scoped_block_swizzler.h
@@ -0,0 +1,40 @@
+// Copyright 2013 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 IOS_CHROME_TEST_BASE_SCOPED_BLOCK_SWIZZLER_H_
+#define IOS_CHROME_TEST_BASE_SCOPED_BLOCK_SWIZZLER_H_
+
+#include <objc/runtime.h>
+
+#include "base/macros.h"
+
+// Helper class that replaces a method implementation with a given block.
+// ScopedBlockSwizzler automatically swizzles when it is constructed and
+// reinstalls the original method implementation when it goes out of scope.
+class ScopedBlockSwizzler {
+ public:
+  // Constructs a new ScopedBlockSwizzler object and replaces the implementation
+  // of |selector| on the |target| class with the given |block|.
+  // ScopedBlockSwizzler first tries to swizzle a class method; if one is not
+  // found, it tries to swizzle an instance method.  It is an error to pass a
+  // |selector| that does not exist on the |target| class.
+  ScopedBlockSwizzler(Class target, SEL selector, id block);
+
+  // Destroys the ScopedBlockSwizzler object, removing the swizzled method and
+  // reinstalling the original method implementation.
+  virtual ~ScopedBlockSwizzler();
+
+ private:
+  // The method that is to be swizzled.  Can be either a class method or an
+  // instance method.
+  Method method_;
+
+  // The original implementation of the swizzled method, saved so that it can be
+  // reinstalled when this object goes out of scope.
+  IMP original_imp_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedBlockSwizzler);
+};
+
+#endif  // IOS_CHROME_TEST_BASE_SCOPED_BLOCK_SWIZZLER_H_