Refactor Library/CompilationUnit and how we define local Scope.

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 8694ef6b7ec80141f3c4964de7b108c03bd480fc..2ebe46b0b7f253edbb3ccec7096562e6f2ceae41 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -190,11 +190,10 @@ void compareWarningKinds(String text, expectedWarnings, foundWarnings) {
 
 void importLibrary(LibraryElement target, LibraryElement imported,
                    Compiler compiler) {
-  for (Link<Element> link = imported.topLevelElements; !link.isEmpty();
-       link = link.tail) {
-    compiler.withCurrentElement(link.head, () {
-        target.define(link.head, compiler);
-      });
+  for (var element in imported.localMembers) {
+    compiler.withCurrentElement(element, () {
+      target.addToScope(element, compiler);
+    });
   }
 }