Lots of frog cleanup

frog/tree.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.
 /**
  * The base type for all nodes in a dart abstract syntax tree.
  */
 class Node {
   /** The source code this [Node] represents. */
   SourceSpan span;
 
   Node(this.span) {}
 
   /** Classic double-dispatch visitor for implementing passes. */
   abstract visit(TreeVisitor visitor);
 
   /** A multiline string showing the node and its children. */
   String toDebugString() {
     var to = new TreeOutput();
     var tp = new TreePrinter(to);
     this.visit(tp);
     return to.buf.toString();
   }
 }
 
 /** Represents all definitions allowed at the top-level. */
 class Definition extends Statement {
   Definition(SourceSpan span): super(span) {}
 
   List<TypeParameter> get typeParameters() => null;
-  String get nativeType() => null;
+  NativeType get nativeType() => null;
 }
 
 /** The base type for statements. */
 class Statement extends Node {
   Statement(SourceSpan span): super(span) {}
 }
 
 /** The base type for expressions. */
 class Expression extends Node {
   Expression(SourceSpan span): super(span) {}
 }
 
+/** The base type for a reference to a [Type]. */
 class TypeReference extends Node {
-  Type type;
-  TypeReference(SourceSpan span, [this.type=null]): super(span) {}
-
-  visit(TreeVisitor visitor) => visitor.visitTypeReference(this);
-
-  bool get isFinal() => false;
+  TypeReference(SourceSpan span): super(span) {}
 }
 
 // TODO(jimhug): Clean-up and factor out of core.
 /** Simple class to provide a textual dump of trees for debugging. */
 class TreeOutput {
   int depth;
   StringBuffer buf;
 
   var printer;
 
@@ skipping 66 matching lines @@
           node.visit(printer);
         } else {
           writeln('null');
         }
       }
       depth -= 1;
       writeln(']');
     }
   }
 }