Add type inference logic for cascade expressions.

pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
index 69f55a3bda86175caf44c142492cc817f64f6ebd..cbc22121465bcf63854865ba5e735f04d7ce020a 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
@@ -78,6 +78,12 @@ class TypeInferenceListener
   void boolLiteralExit(BoolLiteral expression, DartType inferredType) =>
       debugExpressionExit("boolLiteral", expression, inferredType);
 
+  bool cascadeExpressionEnter(Let expression, DartType typeContext) =>
+      debugExpressionEnter("cascade", expression, typeContext);
+
+  void cascadeExpressionExit(Let expression, DartType inferredType) =>
+      debugExpressionExit("cascade", expression, inferredType);
+
   bool conditionalExpressionEnter(
           ConditionalExpression expression, DartType typeContext) =>
       debugExpressionEnter("conditionalExpression", expression, typeContext);