Better error-message when bind fails.

runtime/bin/socket_unsupported.cc

Index: runtime/bin/socket_unsupported.cc
diff --git a/runtime/bin/socket_unsupported.cc b/runtime/bin/socket_unsupported.cc
index 0ea27f1aee0e1c13584b1abe9c87dc1d326b907c..089e48e8967f73e96a198e874139a6ede518a343 100644
--- a/runtime/bin/socket_unsupported.cc
+++ b/runtime/bin/socket_unsupported.cc
@@ -35,6 +35,12 @@ void FUNCTION_NAME(Socket_CreateBindConnect)(Dart_NativeArguments args) {
 }
 
 
+void FUNCTION_NAME(Socket_IsBindError)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewDartArgumentError(
+      "Sockets unsupported on this platform"));
+}
+
+
 void FUNCTION_NAME(Socket_CreateBindDatagram)(Dart_NativeArguments args) {
   Dart_ThrowException(DartUtils::NewDartArgumentError(
       "Sockets unsupported on this platform"));