Extract ClosedWorldRefiner implementation from ClosedWorldImpl to ClosedWorldBase

pkg/compiler/lib/src/closure.dart

Index: pkg/compiler/lib/src/closure.dart
diff --git a/pkg/compiler/lib/src/closure.dart b/pkg/compiler/lib/src/closure.dart
index aae57e5db4236d033e40636e6af7daa22d8ba2f1..908ecce3f2bba1685519424772ae04ca9f959440 100644
--- a/pkg/compiler/lib/src/closure.dart
+++ b/pkg/compiler/lib/src/closure.dart
@@ -53,9 +53,7 @@ class ClosureTask extends CompilerTask {
   /// Create [ClosureClassMap]s for all live members.
   void createClosureClasses(ClosedWorldRefiner closedWorldRefiner) {
     compiler.enqueuer.resolution.processedEntities
-        .forEach((AstElement element) {
-      // TODO(johnniwinther): Typedefs should never be in processedElements.
-      if (element.isTypedef) return;
+        .forEach((MemberElement element) {
       ResolvedAst resolvedAst = element.resolvedAst;
       if (element.isAbstract) return;
       if (element.isField &&