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..9dfbc8ca40e688d5f8350556e0ac276f667c6f46 100644
--- a/net/udp/udp_socket_libevent.h
+++ b/net/udp/udp_socket_libevent.h
@@ -129,6 +129,12 @@ class NET_EXPORT UDPSocketLibevent : public base::NonThreadSafe {
   // Return a network error code.
   int LeaveGroup(const IPAddressNumber& group_address) const;
 
+  // Set interface to use for multicast. If |interface_index| set to 0, default
+  // interface is used.
+  // Should be called before Bind().
+  // Returns a network error code.
+  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.
   // Cannot be negative or more than 255.
@@ -237,6 +243,9 @@ 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_;