Reduce use of elements/resolution_types in enqueuer.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.js.enqueue;
 
 import 'dart:collection' show Queue;
 
 import '../common/codegen.dart' show CodegenWorkItem;
 import '../common/tasks.dart' show CompilerTask;
@@ skipping 184 matching lines @@
         if (_options.enableTypeAssertions) {
           _registerIsCheck(type);
         }
         break;
       case TypeUseKind.TYPE_LITERAL:
         break;
     }
   }
 
   void _registerIsCheck(ResolutionDartType type) {
-    type = _universe.registerIsCheck(type);
-    // Even in checked mode, type annotations for return type and argument
-    // types do not imply type checks, so there should never be a check
-    // against the type variable of a typedef.
-    assert(!type.isTypeVariable || !type.element.enclosingElement.isTypedef);
+    _universe.registerIsCheck(type);
   }
 
   void _registerClosurizedMember(MemberElement element) {
     assert(element.isInstanceMember);
     applyImpact(listener.registerClosurizedMember(element));
   }
 
   void forEach(void f(WorkItem work)) {
     do {
       while (_queue.isNotEmpty) {
@@ skipping 57 matching lines @@
     // code for checked setters.
     if (element.isField && element.isInstanceMember) {
       if (!_options.enableTypeAssertions ||
           element.enclosingElement.isClosure) {
         return null;
       }
     }
     return new CodegenWorkItem(_backend, element);
   }
 }