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

sdk/lib/_internal/compiler/implementation/enqueue.dart

Index: sdk/lib/_internal/compiler/implementation/enqueue.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/enqueue.dart	(revision 14840)
+++ sdk/lib/_internal/compiler/implementation/enqueue.dart	(working copy)
@@ -139,6 +139,10 @@
     }
     universe.instantiatedClasses.add(cls);
     onRegisterInstantiatedClass(cls);
+    if (cls.isAbstract(compiler)) {
+      ClassElement element = compiler.backend.getBackendImplementation(cls);
+      if (element != null) registerInstantiatedClass(element);
+    }
   }
 
   bool checkNoEnqueuedInvokedInstanceMethods() {