Implement FunctionTypeAlias in AstBuilder.

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 8be392c3981576b243f47ca736359b1031082413..6fd0adda9e8af1c0fa5aa95de066b6764d3b0244 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -232,6 +232,12 @@ class Listener {
 
   void beginFunctionTypeAlias(Token token) {}
 
+  /// Handle the end of a typedef declaration.  Substructures:
+  /// - Metadata
+  /// - Return type
+  /// - Name (identifier)
+  /// - Type variables
+  /// - Formal parameters
   void endFunctionTypeAlias(Token typedefKeyword, Token endToken) {
     logEvent("FunctionTypeAlias");
   }