Refactor Library/CompilationUnit and how we define local Scope.

lib/compiler/implementation/world.dart

Index: lib/compiler/implementation/world.dart
diff --git a/lib/compiler/implementation/world.dart b/lib/compiler/implementation/world.dart
index 7254d7a7f68e87537c73a78fe71b319e493d80c8..9652e6702902bc2e9eabcd26cd726e700c16ac2a 100644
--- a/lib/compiler/implementation/world.dart
+++ b/lib/compiler/implementation/world.dart
@@ -19,7 +19,7 @@ class World {
     }
 
     libraries.forEach((LibraryElement library) {
-      for (Link<Element> link = library.topLevelElements;
+      for (Link<Element> link = library.localMembers;
            !link.isEmpty();
            link = link.tail) {
         Element element = link.head;