Add ElementCodegenWorldBuilder

pkg/compiler/lib/src/js_emitter/program_builder/collector.dart

Index: pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart b/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
index 0b062330b1ba78b12618a08e357c719d225ff511..9f654f2ab8a6b05b6c3984b8518d1a20ec6beacd 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
@@ -203,7 +203,7 @@ class Collector {
         .toList());
 
     // Compute needed classes.
-    Set<ClassElement> instantiatedClasses =
+    Set<ClassEntity> instantiatedClasses =
         // TODO(johnniwinther): This should be accessed from a codegen closed
         // world.
         _worldBuilder.directlyInstantiatedClasses
@@ -219,7 +219,7 @@ class Collector {
       }
     }
 
-    void addClassesWithSuperclasses(Iterable<ClassElement> classes) {
+    void addClassesWithSuperclasses(Iterable<ClassEntity> classes) {
       for (ClassElement cls in classes) {
         addClassWithSuperclasses(cls);
       }