fix CombinatorContributor to only suggest public members

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

Index: pkg/analysis_server/test/services/completion/dart/combinator_contributor_test.dart
diff --git a/pkg/analysis_server/test/services/completion/dart/combinator_contributor_test.dart b/pkg/analysis_server/test/services/completion/dart/combinator_contributor_test.dart
index 25e61e4ae3118b14305f0f7658f34261d79bf524..921525bb7b5e91a4f71241347224f43d386f5a6a 100644
--- a/pkg/analysis_server/test/services/completion/dart/combinator_contributor_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/combinator_contributor_test.dart
@@ -94,7 +94,8 @@ class CombinatorContributorTest extends DartCompletionContributorTest {
       library libAB;
       part '/partAB.dart';
       class A { }
-      class B { }''');
+      class B { }
+      class _AB''');
     addSource(
         '/partAB.dart',
         '''
@@ -124,6 +125,7 @@ class CombinatorContributorTest extends DartCompletionContributorTest {
     assertSuggestClass('B',
         relevance: DART_RELEVANCE_DEFAULT,
         kind: CompletionSuggestionKind.IDENTIFIER);
+    assertNotSuggested('_AB');
     assertSuggestClass('PB',
         relevance: DART_RELEVANCE_DEFAULT,
         kind: CompletionSuggestionKind.IDENTIFIER);