Move registering of interceptors to the JsBackend.

lib/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.
 
 class ElementAst {
   final Node ast;
   final TreeElements treeElements;
 
   ElementAst(this.ast, this.treeElements);
 
@@ skipping 171 matching lines @@
     }
     return true;
   }
 
   DartBackend(Compiler compiler, List<String> strips)
       : tasks = <CompilerTask>[],
         forceStripTypes = strips.indexOf('types') != -1,
         stripAsserts = strips.indexOf('asserts') != -1,
         super(compiler);
 
+  Element getInterceptor(Selector selector) => null;
+
   void enqueueHelpers(Enqueuer world) {
     // Right now resolver doesn't always resolve interfaces needed
     // for literals, so force them. TODO(antonm): fix in the resolver.
     final LITERAL_TYPE_NAMES = const [
       'Map', 'List', 'num', 'int', 'double', 'bool'
     ];
     final coreLibrary = compiler.coreLibrary;
     for (final name in LITERAL_TYPE_NAMES) {
       ClassElement classElement = coreLibrary.findLocal(new SourceString(name));
       classElement.ensureResolved(compiler);
@@ skipping 332 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().uri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Collection<Element> elements) =>
     sorted(elements, compareElements);