New parser event needed to check case expressions.

pkg/front_end/lib/src/fasta/parser/listener.dart

Index: pkg/front_end/lib/src/fasta/parser/listener.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/listener.dart b/pkg/front_end/lib/src/fasta/parser/listener.dart
index 95a35ea679bf3c828d6b9c78443908b9e55a6100..47cb4ff3e848f33bd8bee01a9846d7e7b76c0545 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -65,6 +65,12 @@ class Listener {
     logEvent("Cascade");
   }
 
+  void beginCaseExpression(Token caseKeyword) {}
+
+  void endCaseExpression(Token colon) {
+    logEvent("CaseExpression");
+  }
+
   void beginClassBody(Token token) {}
 
   /// Handle the end of the body of a class declaration.  The only substructures