Revert "Make Comparable generic."

sdk/lib/collection/splay_tree.dart

 // Copyright (c) 2012, 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.
 
 part of dart.collection;
 
 /**
  * A node in a splay tree. It holds the key, the value and the left
  * and right children in the tree.
  */
 class SplayTreeNode<K, V> {
   final K key;
   V value;
   SplayTreeNode<K, V> left;
   SplayTreeNode<K, V> right;
 
   SplayTreeNode(K this.key, V this.value);
 }
 
 /**
  * A splay tree is a self-balancing binary
  * search tree with the additional property that recently accessed
  * elements are quick to access again. It performs basic operations
  * such as insertion, look-up and removal in O(log(n)) amortized time.
  *
  * This implementation is a Dart version of the JavaScript
  * implementation in the V8 project.
  */
-class SplayTreeMap<K extends Comparable<K>, V> implements Map<K, V> {
+class SplayTreeMap<K extends Comparable, V> implements Map<K, V> {
 
   // The root node of the splay tree. It will contain either the last
   // element inserted, or the last element looked up.
   SplayTreeNode<K, V> _root;
 
   // The dummy node used when performing a splay on the tree. It is a
   // local field of the class to avoid allocating a node each time a
   // splay is performed.
   SplayTreeNode<K, V> _dummy;
 
@@ skipping 414 matching lines @@
 class _SplayTreeValueIterator<K, V> extends _SplayTreeIterator<V> {
   _SplayTreeValueIterator(SplayTreeMap<K, V> map): super(map);
   V _getValue(SplayTreeNode node) => node.value;
 }
 
 class _SplayTreeNodeIterator<K, V>
     extends _SplayTreeIterator<SplayTreeNode<K, V>> {
   _SplayTreeNodeIterator(SplayTreeMap<K, V> map): super(map);
   SplayTreeNode<K, V> _getValue(SplayTreeNode node) => node;
 }