Reapply "Refactor constant part." (r4958) with fixes.

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 711 matching lines @@
 
 class DartString implements Iterable<int> {
   factory DartString.literal(String string) => new LiteralDartString(string);
   factory DartString.rawString(SourceString source, int length) =>
       new RawSourceDartString(source, length);
   factory DartString.escapedString(SourceString source, int length) =>
       new EscapedSourceDartString(source, length);
   DartString();
   abstract int get length();
   bool isEmpty() => length == 0;
-  // TODO(lrn): Is this test too expensive?
-  bool definitelyEquals(DartString other) => toString() == other.toString();
   abstract Iterator<int> iterator();
   abstract String toString();
 
   bool operator ==(var other) {
     if (other is !DartString) return false;
     DartString otherString = other;
     if (length != otherString.length) return false;
     Iterator it1 = iterator();
     Iterator it2 = otherString.iterator();
     while (it1.hasNext()) {
@@ skipping 940 matching lines @@
   static bool isConstructorRedirect(Send node) {
     return (node.receiver === null &&
             node.selector.asIdentifier() !== null &&
             node.selector.asIdentifier().isThis()) ||
            (node.receiver !== null &&
             node.receiver.asIdentifier() !== null &&
             node.receiver.asIdentifier().isThis() &&
             node.selector.asIdentifier() !== null);
   }
 }