Add IPAddress class as a replacement for the IPAddressNumber typedef.

net/base/ip_address_number.h

Index: net/base/ip_address_number.h
diff --git a/net/base/ip_address_number.h b/net/base/ip_address_number.h
index b1058758d9d1f3b91c7d4dfb264369b5b54a17ea..bce3c980fde53255649b964793304c9c4c120122 100644
--- a/net/base/ip_address_number.h
+++ b/net/base/ip_address_number.h
@@ -19,6 +19,10 @@ namespace net {
 // network byte ordering.
 //
 // IPv4 addresses will have length 4, whereas IPv6 address will have length 16.
+//
+// TODO(Martijnc): Remove the IPAddressNumber typedef. New code should use
+// IPAddress instead and existing code should be switched over.
+// https://crbug.com/496258
 typedef std::vector<unsigned char>
     IPAddressNumber;  // This is also duplicated in net_util.h
 typedef std::vector<IPAddressNumber> IPAddressList;