Revert "Collect the types used in is-checks in the resolver phase."

lib/compiler/implementation/util/link_implementation.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.
 
 class LinkIterator<T> implements Iterator<T> {
   Link<T> current;
   LinkIterator(Link<T> this.current);
   bool hasNext() => !current.isEmpty();
   T next() {
     T result = current.head;
@@ skipping 52 matching lines @@
   Link<T> reversePrependAll(Link<T> from) {
     if (from.isEmpty()) return this;
     return this.prepend(from.head).reversePrependAll(from.tail);
   }
 
   List toList() => const [];
 
   bool isEmpty() => true;
 
   void forEach(void f(T element)) {}
-
-  bool equals(other) {
-    if (other is !Link<T>) return false;
-    return other.isEmpty();
-  }
 }
 
 class LinkEntry<T> implements Link<T> {
   final T head;
   Link<T> tail;
 
   LinkEntry(T this.head, Link<T> this.tail);
 
   Link<T> prepend(T element) {
     // TODO(ahe): Use new Link<T>, but this cost 8% performance on VM.
@@ skipping 44 matching lines @@
       list.addLast(link.head);
     }
     return list;
   }
 
   void forEach(void f(T element)) {
     for (Link<T> link = this; !link.isEmpty(); link = link.tail) {
       f(link.head);
     }
   }
-
-  bool equals(other) {
-    if (other is !Link<T>) return false;
-    Link<T> myElements = this;
-    while (!myElements.isEmpty() && !other.isEmpty()) {
-      if (myElements.head != other.head) {
-        return false;
-      }
-      myElements = myElements.tail;
-      other = other.tail;
-    }
-    return myElements.isEmpty() && other.isEmpty();
-  }
 }
 
 class LinkBuilderImplementation<T> implements LinkBuilder<T> {
   LinkEntry<T> head = null;
   LinkEntry<T> lastLink = null;
   int length = 0;
 
   LinkBuilderImplementation();
 
   Link<T> toLink() {
     if (head === null) return const LinkTail();
     lastLink.tail = const LinkTail();
     Link<T> link = head;
     lastLink = null;
     head = null;
     return link;
   }
 
   void addLast(T t) {
     length++;
     LinkEntry<T> entry = new LinkEntry<T>(t, null);
     if (head === null) {
       head = entry;
     } else {
       lastLink.tail = entry;
     }
     lastLink = entry;
   }
 }