Port the remaining of dart:core to the unified corelib.

lib/compiler/implementation/world.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.
 
 class World {
   final Map<ClassElement, Set<ClassElement>> subtypes;
 
   World() : subtypes = new Map<ClassElement, Set<ClassElement>>();
 
   void populate(Compiler compiler, Collection<LibraryElement> libraries) {
     void addSubtypes(ClassElement cls) {
       for (Type type in cls.allSupertypes) {
         Set<Element> subtypesOfCls = subtypes.putIfAbsent(
           type.element,
           () => new Set<ClassElement>());
         subtypesOfCls.add(cls);
       }
     }
 
     libraries.forEach((LibraryElement library) {
       for (Link<Element> link = library.topLevelElements;
            !link.isEmpty();
            link = link.tail) {
         Element element = link.head;
-        if (!element.isClass()) continue;
+        if (!element.isClass() || compiler.isPatchElement(element)) continue;
         ClassElement cls = element;
         compiler.resolveClass(cls);
         addSubtypes(cls);
       }
     });
   }
 
   /**
    * Returns a [MemberSet] that contains the possible targets of a
    * selector named [member] on a receiver whose type is [type].
@@ skipping 43 matching lines @@
   final SourceString name;
 
   MemberSet(SourceString this.name) : elements = new Set<Element>();
 
   void add(Element element) {
     elements.add(element);
   }
 
   bool isEmpty() => elements.isEmpty();
 }