Refactor Library/CompilationUnit and how we define local Scope.

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 {
   Compiler compiler;  // Set in populate().
   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;
+      for (Element element in library.localMembers) {
         if (!element.isClass()) continue;
         ClassElement cls = element;
         compiler.resolveClass(cls);
         addSubtypes(cls);
       }
     });
 
     // Mark the world as populated.
     assert(compiler !== null);
     this.compiler = compiler;
@@ skipping 62 matching lines @@
   final SourceString name;
 
   MemberSet(SourceString this.name) : elements = new Set<Element>();
 
   void add(Element element) {
     elements.add(element);
   }
 
   bool isEmpty() => elements.isEmpty();
 }