Implemented AddAllocWithZoneMethod to override allocWithZone: on demand.

ios/web/alloc_with_zone_interceptor.h

Index: ios/web/alloc_with_zone_interceptor.h
diff --git a/ios/web/alloc_with_zone_interceptor.h b/ios/web/alloc_with_zone_interceptor.h
new file mode 100644
index 0000000000000000000000000000000000000000..00265405d748091e0c3ec64f9f42109e1502bddf
--- /dev/null
+++ b/ios/web/alloc_with_zone_interceptor.h
@@ -0,0 +1,18 @@
+// Copyright 2015 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_WEB_ALLOC_WITH_ZONE_INTERCEPTOR_H_
+#define IOS_WEB_ALLOC_WITH_ZONE_INTERCEPTOR_H_
+
+#import <Foundation/Foundation.h>
+
+namespace web {
+// Adds |impl_block| as a custom implementation for |allocWithZone:| method of
+// |target| Class. AddAllocWithZoneMethod can not swizzle existing
+// |allocWithZone:| method of |target| Class. Neither |target| nor any of its
+// superclases must not have overridden |allocWithZone:|.
+void AddAllocWithZoneMethod(Class target, id (^impl_block)(Class, NSZone*));
+}  // namespace web
+
+#endif  // IOS_WEB_ALLOC_WITH_ZONE_INTERCEPTOR_H_