Better error message for missing async with await

pkg/analysis_server/test/services/correction/fix_test.dart

Index: pkg/analysis_server/test/services/correction/fix_test.dart
diff --git a/pkg/analysis_server/test/services/correction/fix_test.dart b/pkg/analysis_server/test/services/correction/fix_test.dart
index 2f0e0bcdc7e553af3e06ea2b4b1927ca9a602e9d..647fc12fdfdca29d354d6dd732fdb5ad35b8579d 100644
--- a/pkg/analysis_server/test/services/correction/fix_test.dart
+++ b/pkg/analysis_server/test/services/correction/fix_test.dart
@@ -472,7 +472,7 @@ main() {
     // Has fix for "await".
     {
       AnalysisError error = errors[1];
-      expect(error.message, startsWith("Undefined name 'await'."));
+      expect(error.message, startsWith("Undefined name 'await' in function"));
       List<Fix> fixes = await _computeFixes(error);
       // has exactly one fix
       expect(fixes, hasLength(1));