Add type info to fix analyzer failures for 1.23.0-dev.5.0

lib/src/runner/load_suite.dart

Index: lib/src/runner/load_suite.dart
diff --git a/lib/src/runner/load_suite.dart b/lib/src/runner/load_suite.dart
index 7034de442cd9a75bf16f3fa7720d17652c5310fc..f8811bcbb1e50f3a9c62308fe1ceedc5202614b1 100644
--- a/lib/src/runner/load_suite.dart
+++ b/lib/src/runner/load_suite.dart
@@ -66,7 +66,8 @@ class LoadSuite extends Suite implements RunnerSuite {
   ///
   /// If the the load test is closed before [body] is complete, it will close
   /// the suite returned by [body] once it completes.
-  factory LoadSuite(String name, SuiteConfiguration config, body(),
+  factory LoadSuite(
+      String name, SuiteConfiguration config, FutureOr<RunnerSuite> body(),
       {String path, TestPlatform platform}) {
     var completer = new Completer<Pair<RunnerSuite, Zone>>.sync();
     return new LoadSuite._(name, config, () {