Remove unused API.

dart/sdk/lib/_internal/compiler/implementation/dart_backend/backend.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 dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 206 matching lines @@
         new Selector.call("toString", null, 0));
     world.registerInvokedGetter(
         new Selector.getter("hashCode", null));
     world.registerInvocation(
         new Selector.binaryOperator("=="));
     world.registerInvocation(
         new Selector.call("compareTo", null, 1));
   }
 
   void codegen(CodegenWorkItem work) { }
-  void processNativeClasses(Enqueuer world,
-                            Iterable<LibraryElement> libraries) { }
 
   bool isUserLibrary(LibraryElement lib) {
     final INTERNAL_HELPERS = [
       compiler.jsHelperLibrary,
       compiler.interceptorsLibrary,
     ];
     return INTERNAL_HELPERS.indexOf(lib) == -1 && !lib.isPlatformLibrary;
   }
 
   void assembleProgram() {
@@ skipping 393 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().canonicalUri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Iterable<Element> elements) =>
     sorted(elements, compareElements);