Add support for parsing #void with Fasta.

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 3c6c2365179399396962f6d2da3f7582e1bc2201..633ef962780ee115d46986eae80436965622d9c5 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -875,6 +875,10 @@ class Listener {
     logEvent("Operator");
   }
 
+  void handleSymbolVoid(Token token) {
+    logEvent("SymbolVoid");
+  }
+
   /// Handle the end of a construct of the form "operator <token>".
   void handleOperatorName(Token operatorKeyword, Token token) {
     logEvent("OperatorName");