Multicast DNS implementation (initial)

net/dns/dns_protocol.h

Index: net/dns/dns_protocol.h
diff --git a/net/dns/dns_protocol.h b/net/dns/dns_protocol.h
index b65f56dc2b52ccd0a0988b719dbc139da29ef831..4516b2914f48e5b57bc804dd4f3221bfd7c5f443 100644
--- a/net/dns/dns_protocol.h
+++ b/net/dns/dns_protocol.h
@@ -13,6 +13,7 @@ namespace net {
 namespace dns_protocol {
 
 static const uint16 kDefaultPort = 53;
+static const uint16 kDefaultPortMulticast = 5353;
 
 // DNS packet consists of a header followed by questions and/or answers.
 // For the meaning of specific fields, please see RFC 1035 and 2535
@@ -101,6 +102,10 @@ static const int kMaxNameLength = 255;
 // bytes (not counting the IP nor UDP headers).
 static const int kMaxUDPSize = 512;
 
+// RFC 6762, section 17: Messages over the local link are restricted by the
+// medium's MTU, and must be under 9000 bytes
+static const int kMaxMulticastSize = 9000;
+
 // DNS class types.
 static const uint16 kClassIN = 1;