Implement type inference for symbol literals.

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 c8b3f3588f7f6ca56d900c835350a46c6aac5448..c447eb7610423b4a986b9e9fc9503f1877a47a7b 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
@@ -340,6 +340,12 @@ class TypeInferenceListener
   void switchStatementExit(SwitchStatement statement) =>
       debugStatementExit('switchStatement', statement);
 
+  bool symbolLiteralEnter(SymbolLiteral expression, DartType typeContext) =>
+      debugExpressionEnter("symbolLiteral", expression, typeContext);
+
+  void symbolLiteralExit(SymbolLiteral expression, DartType inferredType) =>
+      debugExpressionExit("symbolLiteral", expression, inferredType);
+
   bool throwEnter(Throw expression, DartType typeContext) =>
       debugExpressionEnter('throw', expression, typeContext);