Generate an error for active connections when the HTTP client is shutdown

tests/standalone/io/http_session_test.dart

Index: tests/standalone/io/http_session_test.dart
diff --git a/tests/standalone/io/http_session_test.dart b/tests/standalone/io/http_session_test.dart
index 2b7f81c6080d2b60203f9cfcfc6fe6bc2faa99ce..1538c2c56e12a7d84fbff8fca1e6b6df8d2ff3ad 100644
--- a/tests/standalone/io/http_session_test.dart
+++ b/tests/standalone/io/http_session_test.dart
@@ -30,8 +30,11 @@ Future<String> connectGetSession(int port, [String session]) {
     request.outputStream.close();
   };
   conn.onResponse = (response) {
-    client.shutdown();
-    c.complete(getSessionId(response.cookies));
+    response.inputStream.onData = response.inputStream.read;
+    response.inputStream.onClosed = () {
+      client.shutdown();
+      c.complete(getSessionId(response.cookies));
+    };
   };
   return c.future;
 }