Better error-message when bind fails.

runtime/bin/socket.h

Index: runtime/bin/socket.h
diff --git a/runtime/bin/socket.h b/runtime/bin/socket.h
index 0b17706446bb6637ba9e48a2013f17fc76c91620..6a50d796da61ab37c81820a7c5098ef07dba7cca 100644
--- a/runtime/bin/socket.h
+++ b/runtime/bin/socket.h
@@ -278,6 +278,9 @@ class Socket {
   // specified as the port component of the passed RawAddr structure.
   static intptr_t CreateBindConnect(const RawAddr& addr,
                                     const RawAddr& source_addr);
+  // Returns true if the given error-number is because the system was not able
+  // to bind the socket to a specific IP.
+  static bool IsBindError(intptr_t error_number);
   // Creates a datagram socket which is bound. The port to bind
   // to is specified as the port component of the RawAddr structure.
   static intptr_t CreateBindDatagram(const RawAddr& addr, bool reuseAddress);