Rename Universe to WorldBuilder.

pkg/compiler/lib/src/js_backend/runtime_types.dart

Index: pkg/compiler/lib/src/js_backend/runtime_types.dart
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index f465f76b23fbfb375c1578617ce0f415be1e755c..d3adc4bb207a2e3cc4f6729679cab872d4f230ac 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -46,7 +46,7 @@ abstract class RuntimeTypes {
   ///
   /// This function must be called after all is-checks have been registered.
   void addImplicitChecks(
-      Universe universe, Iterable<ClassElement> classesUsingChecks);
+      WorldBuilder universe, Iterable<ClassElement> classesUsingChecks);
 
   /// Return all classes that are referenced in the type of the function, i.e.,
   /// in the return type or the argument types.
@@ -170,7 +170,7 @@ class _RuntimeTypes implements RuntimeTypes {
    */
   @override
   void addImplicitChecks(
-      Universe universe, Iterable<ClassElement> classesUsingChecks) {
+      WorldBuilder universe, Iterable<ClassElement> classesUsingChecks) {
     // If there are no classes that use their variables in checks, there is
     // nothing to do.
     if (classesUsingChecks.isEmpty) return;
@@ -364,7 +364,8 @@ class _RuntimeTypes implements RuntimeTypes {
         computeChecks(allInstantiatedArguments, checkedArguments);
   }
 
-  Set<DartType> computeInstantiatedTypesAndClosures(CodegenUniverse universe) {
+  Set<DartType> computeInstantiatedTypesAndClosures(
+      CodegenWorldBuilder universe) {
     Set<DartType> instantiatedTypes =
         new Set<DartType>.from(universe.instantiatedTypes);
     for (DartType instantiatedType in universe.instantiatedTypes) {