improve annotation argument completion - from https://github.com/dart-lang/sdk/pull/25099

pkg/analysis_server/test/services/completion/arglist_contributor_test.dart

Index: pkg/analysis_server/test/services/completion/arglist_contributor_test.dart
diff --git a/pkg/analysis_server/test/services/completion/arglist_contributor_test.dart b/pkg/analysis_server/test/services/completion/arglist_contributor_test.dart
index 9bb8aa73506d61737fc2c7a94cd08b24752f1cfa..3ac4409621f7698e8ceefadf4d25ae6efcbe2ab3 100644
--- a/pkg/analysis_server/test/services/completion/arglist_contributor_test.dart
+++ b/pkg/analysis_server/test/services/completion/arglist_contributor_test.dart
@@ -91,7 +91,6 @@ class ArgListContributorTest extends AbstractCompletionTest {
   }
 
   test_Annotation_local_constructor_named_param() {
-    //
     addTestSource('''
 class A { A({int one, String two: 'defaultValue'}) { } }
 @A(^) main() { }''');
@@ -101,6 +100,16 @@ class A { A({int one, String two: 'defaultValue'}) { } }
     });
   }
 
+  test_Annotation_imported_constructor_named_param() {
+    addSource('/libA.dart', '''
+library libA; class A { A({int one, String two: 'defaultValue'}) { } }''');
+    addTestSource('import "/libA.dart"; @A(^) main() { }');
+    computeFast();
+    return computeFull((bool result) {
+      assertSuggestArguments(namedArguments: ['one','two']);
+    });
+  }
+
   test_ArgumentList_getter() {
     addTestSource('class A {int get foo => 7; main() {foo(^)}');
     computeFast();