Start new design for interceptors and implement String.charCodeAt with it.

sdk/lib/_internal/compiler/implementation/enqueue.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.
 
 part of dart2js;
 
 class EnqueueTask extends CompilerTask {
   final Enqueuer codegen;
   final Enqueuer resolution;
 
@@ skipping 121 matching lines @@
 
   void registerInstantiatedClass(ClassElement cls) {
     if (cls.isInterface()) {
       compiler.internalErrorOnElement(
           // Use the current element, as this is where cls is referenced from.
           compiler.currentElement,
           'Expected a class, but $cls is an interface.');
     }
     universe.instantiatedClasses.add(cls);
     onRegisterInstantiatedClass(cls);
+    if (cls.isAbstract(compiler)) {
+      ClassElement element = compiler.backend.getBackendImplementation(cls);
+      if (element != null) registerInstantiatedClass(element);
+    }
   }
 
   bool checkNoEnqueuedInvokedInstanceMethods() {
     task.measure(() {
       // Run through the classes and see if we need to compile methods.
       for (ClassElement classElement in universe.instantiatedClasses) {
         for (ClassElement currentClass = classElement;
              currentClass != null;
              currentClass = currentClass.superclass) {
           processInstantiatedClass(currentClass);
@@ skipping 214 matching lines @@
 
   String toString() => 'Enqueuer($name)';
 
   registerUsedSelector(Selector selector) {
     Element interceptor = compiler.backend.getInterceptor(selector);
     if (interceptor != null) {
       registerStaticUse(interceptor);
     }
   }
 }