Add support for parsing #void with Fasta.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

Index: pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
index 8eda5e59bbc29abcd5398edbc659b47ca61eace5..e6a2afea2c9c2b0ac3c18b63117bc0384b4b0144 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
@@ -275,6 +275,11 @@ class AstBuilder extends ScopeListener {
     push(toAnalyzerToken(token));
   }
 
+  void handleSymbolVoid(Token token) {
+    debugEvent("SymbolVoid");
+    push(toAnalyzerToken(token));
+  }
+
   void handleBinaryExpression(Token token) {
     debugEvent("BinaryExpression");
     if (identical(".", token.stringValue) ||