Add support of IP_MULTICAST_IF in UDP sockets.

net/udp/udp_socket_libevent.h

Index: net/udp/udp_socket_libevent.h
diff --git a/net/udp/udp_socket_libevent.h b/net/udp/udp_socket_libevent.h
index 6e737de38402d19f7ff1409fb2baffc520cee141..df9c60dba767ca5c719a7be7c7b45c91cc7d3fec 100644
--- a/net/udp/udp_socket_libevent.h
+++ b/net/udp/udp_socket_libevent.h
@@ -118,7 +118,7 @@ class NET_EXPORT UDPSocketLibevent : public base::NonThreadSafe {
   // |group_address| is the group address to join, could be either
   // an IPv4 or IPv6 address.
   // Return a network error code.
-  int JoinGroup(const IPAddressNumber& group_address) const;
+  int JoinGroup(const IPAddressNumber& group_address);
 
   // Leave the multicast group.
   // |group_address| is the group address to leave, could be either
@@ -127,7 +127,11 @@ class NET_EXPORT UDPSocketLibevent : public base::NonThreadSafe {
   // It's optional to leave the multicast group before destroying
   // the socket. It will be done by the OS.
   // Return a network error code.
-  int LeaveGroup(const IPAddressNumber& group_address) const;
+  int LeaveGroup(const IPAddressNumber& group_address);
+
+  // Set interface to use for multicast. If |interface_index| set to 0, default
+  // interface is used. Must be called before |JoinGroup| or |LeaveGroup|.
+  int SetMulticastInterface(uint32 interface_index);
 
   // Set the time-to-live option for UDP packets sent to the multicast
   // group address. The default value of this option is 1.
@@ -237,6 +241,9 @@ class NET_EXPORT UDPSocketLibevent : public base::NonThreadSafe {
   // options that should be applied to |socket_| before Bind().
   int socket_options_;
 
+  // Multicast interface.
+  uint32 multicast_interface_;
+
   // Multicast socket options cached for SetSocketOption.
   // Cannot be used after Bind().
   int multicast_time_to_live_;