Allow plugins to provide completions for non-dart files

pkg/analysis_server/test/integration/completion/get_suggestions_test.dart

Index: pkg/analysis_server/test/integration/completion/get_suggestions_test.dart
diff --git a/pkg/analysis_server/test/integration/completion/get_suggestions_test.dart b/pkg/analysis_server/test/integration/completion/get_suggestions_test.dart
index 25619b43ab8e8dfe6c02177dd4ed19e0fc02bc9b..545735b046cb30df9a301821b58aaf988260048e 100644
--- a/pkg/analysis_server/test/integration/completion/get_suggestions_test.dart
+++ b/pkg/analysis_server/test/integration/completion/get_suggestions_test.dart
@@ -118,7 +118,7 @@ main() {
       // Exception expected
       return errorToken;
     }).then((result) {
-      expect(result, same(errorToken));
+      expect(result, new isInstanceOf<CompletionGetSuggestionsResult>());
     });
   }
 }