Implement super calls.

frog/leg/tree/nodes.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
   R visitCatchBlock(CatchBlock node);
   R visitClassNode(ClassNode node);
   R visitConditional(Conditional node);
@@ skipping 638 matching lines @@
 class Identifier extends Expression {
   final Token token;
 
   SourceString get source() => token.value;
 
   Identifier(Token this.token);
   Identifier.synthetic(String name) : token = new StringToken(null, name, null);
 
   bool isThis() => source.stringValue == 'this';
 
+  bool isSuper() => source.stringValue == 'super';
+
   Identifier asIdentifier() => this;
 
   accept(Visitor visitor) => visitor.visitIdentifier(this);
 
   visitChildren(Visitor visitor) {}
 
   Token getBeginToken() => token;
 
   Token getEndToken() => token;
 }
@@ skipping 566 matching lines @@
 
   visitChildren(Visitor visitor) {
     formals.accept(visitor);
     block.accept(visitor);
   }
 
   Token getBeginToken() => catchKeyword;
 
   Token getEndToken() => block.getEndToken();
 }