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..c8cd1c2657e326f9311c33c1b8dfe6bfa23361be
--- /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. |target| or 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_