Implement dynamic function checks.

dart/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

 // Copyright (c) 2011, 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.
 
 part of js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer implements ClosureNamer {
@@ skipping 454 matching lines @@
   }
 
   /**
    * Returns name of accessor (root to getter and setter) for an instance field.
    */
   String instanceFieldAccessorName(Element element) {
     String proposedName = privateName(element.getLibrary(), element.name);
     return getMappedInstanceName(proposedName);
   }
 
+  String readTypeVariableName(TypeVariableElement element) {
+    return '\$tv_${instanceFieldAccessorName(element)}';
+  }
+
   /**
    * Returns name of the JavaScript property used to store an instance field.
    */
   String instanceFieldPropertyName(Element element) {
     if (element.hasFixedBackendName()) {
       return element.fixedBackendName();
     }
     // If a class is used anywhere as a mixin, we must make the name unique so
     // that it does not accidentally shadow.  Also, the mixin name must be
     // constant over all mixins.
@@ skipping 891 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(link.head);
         first = true;
       }
     }
   }
 }