Move frog/leg to lib/compiler/implementation.

frog/leg/tree/tree.dart

Index: frog/leg/tree/tree.dart
===================================================================
--- frog/leg/tree/tree.dart	(revision 5925)
+++ frog/leg/tree/tree.dart	(working copy)
@@ -1,14 +0,0 @@
-// 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.
-
-#library('tree');
-
-#import('../scanner/scannerlib.dart');
-#import('../util/util.dart');
-#import('../util/characters.dart');
-
-#source('nodes.dart');
-#source('dartstring.dart');
-#source('unparser.dart');
-#source('visitors.dart');