Throw an error if the ServerSocket host argument is invalid.

tests/standalone/io/socket_exception_test.dart

Index: tests/standalone/io/socket_exception_test.dart
diff --git a/tests/standalone/io/socket_exception_test.dart b/tests/standalone/io/socket_exception_test.dart
index 924822dae3e93571c9dd2fd9ac5515a557d15311..0a8ea889235b34fcbf1154f7f2d489d2ba086b34 100644
--- a/tests/standalone/io/socket_exception_test.dart
+++ b/tests/standalone/io/socket_exception_test.dart
@@ -28,6 +28,10 @@ class SocketExceptionTest {
     }
     Expect.equals(false, exceptionCaught);
     Expect.equals(true, !wrongExceptionCaught);
+
+    // Test invalid host.
+    Expect.throws(() => new ServerSocket("__INVALID_HOST__", PORT, 10),
+                  (e) => e is SocketIOException);
   }
 
   static void clientSocketExceptionTest() {
@@ -198,6 +202,7 @@ class SocketExceptionTest {
     clientSocketExceptionTest();
     indexOutOfRangeExceptionTest();
     unknownHostTest();
+
     // TODO(sgjesse): This test seems to fail on the buildbot.
     //unresponsiveHostTest();
   }