Fix hints and warnings.

pkg/front_end/lib/src/fasta/analyzer/mock_type.dart

Index: pkg/front_end/lib/src/fasta/analyzer/mock_type.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/mock_type.dart b/pkg/front_end/lib/src/fasta/analyzer/mock_type.dart
index d2c33afec4b003312b51ee9f3ef924e18a741c13..ce34190cd9d8900ff910e3078d3d10a92988ade4 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/mock_type.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/mock_type.dart
@@ -22,6 +22,8 @@ abstract class MockType extends DartType {
 
   bool get isDartAsyncFuture => internalError("not supported.");
 
+  bool get isDartAsyncFutureOr => internalError("not supported.");
+
   bool get isDartCoreFunction => internalError("not supported.");
 
   bool get isDynamic => internalError("not supported.");