Test for 'search.findElementReferences' for the case when there is no element.

pkg/analysis_server/test/search/element_references_test.dart

Index: pkg/analysis_server/test/search/element_references_test.dart
diff --git a/pkg/analysis_server/test/search/element_references_test.dart b/pkg/analysis_server/test/search/element_references_test.dart
index 38ada0ea46e8b50bbfa4521a8d7028a439d95184..e7276900a5839258dfc2dce2275252971ca4598f 100644
--- a/pkg/analysis_server/test/search/element_references_test.dart
+++ b/pkg/analysis_server/test/search/element_references_test.dart
@@ -26,7 +26,9 @@ class ElementReferencesTest extends AbstractSearchDomainTest {
   Future findElementReferences(String search, bool includePotential) {
     int offset = findOffset(search);
     return waitForTasksFinished().then((_) {
-      Request request = new SearchFindElementReferencesParams(testFile, offset,
+      Request request = new SearchFindElementReferencesParams(
+          testFile,
+          offset,
           includePotential).toRequest('0');
       Response response = handleSuccessfulRequest(request);
       var result = new SearchFindElementReferencesResult.fromResponse(response);
@@ -299,6 +301,17 @@ main() {
     });
   }
 
+  test_noElement() {
+    addTestFile('''
+main() {
+  print(noElement);
+}
+''');
+    return findElementReferences('noElement', false).then((_) {
+      expect(searchId, isNull);
+    });
+  }
+
   test_oneUnit_twoLibraries() {
     var pathA = '/project/bin/libA.dart';
     var pathB = '/project/bin/libB.dart';