Fix error handling for formatting and update the spec

pkg/analysis_server/test/edit/format_test.dart

Index: pkg/analysis_server/test/edit/format_test.dart
diff --git a/pkg/analysis_server/test/edit/format_test.dart b/pkg/analysis_server/test/edit/format_test.dart
index 1bd9f709d35503b5522f35cddb4eca40e486dabd..b045e1a19d339082db3e4aa66ed01480a957bd37 100644
--- a/pkg/analysis_server/test/edit/format_test.dart
+++ b/pkg/analysis_server/test/edit/format_test.dart
@@ -13,6 +13,7 @@ import 'package:analyzer/src/plugin/plugin_impl.dart';
 import 'package:unittest/unittest.dart' hide ERROR;
 
 import '../analysis_abstract.dart';
+import '../mocks.dart';
 import '../reflective_tests.dart';
 
 main() {
@@ -87,6 +88,17 @@ main() {
     });
   }
 
+  Future test_withErrors() {
+    addTestFile('''
+main() { int x = 
+''');
+    return waitForTasksFinished().then((_) {
+      Request request = new EditFormatParams(testFile, 0, 3).toRequest('0');
+      Response response = handler.handleRequest(request);
+      expect(response, isResponseFailure('0'));
+    });
+  }
+
   EditFormatResult _formatAt(int selectionOffset, int selectionLength) {
     Request request = new EditFormatParams(
         testFile, selectionOffset, selectionLength).toRequest('0');