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 424 matching lines @@
    * Returns the internal name used for an invocation mirror of this selector.
    */
   String invocationMirrorInternalName(Selector selector)
       => invocationName(selector);
 
   String instanceFieldName(Element element) {
     String proposedName = privateName(element.getLibrary(), element.name);
     return getMappedInstanceName(proposedName);
   }
 
+  String readTypeVariableName(TypeVariableElement element) {
+    return '\$tv_${instanceFieldName(element)}';
+  }
+
   // Construct a new name for the element based on the library and class it is
   // in.  The name here is not important, we just need to make sure it is
   // unique.  If we are minifying, we actually construct the name from the
   // minified versions of the class and instance names, but the result is
   // minified once again, so that is not visible in the end result.
   String shadowedFieldName(Element fieldElement) {
     // Check for following situation: Native field ${fieldElement.name} has
     // fixed JSName ${fieldElement.nativeName()}, but a subclass shadows this
     // name.  We normally handle that by renaming the superclass field, but we
     // can't do that because native fields have fixed JavaScript names.
@@ skipping 880 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(link.head);
         first = true;
       }
     }
   }
 }