Delete dart_backend from compiler.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

 // Copyright (c) 2013, 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.
 
 library analyze_unused_dart2js;
 
 import 'package:async_helper/async_helper.dart';
 
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/messages.dart';
 import 'package:compiler/src/filenames.dart';
 
 import 'analyze_helper.dart';
 
 // Do not remove WHITE_LIST even if it's empty.  The error message for
 // unused members refers to WHITE_LIST by name.
 const Map<String, List<String>> WHITE_LIST = const {
   // Helper methods for debugging should never be called from production code:
   "lib/src/helpers/": const [" is never "],
 
   // Node.asAssert, Node.asLiteralBool is never used.
   "lib/src/tree/nodes.dart": const [
       "The method 'asAssert' is never called.",
       "The method 'asLiteralBool' is never called."],
 
-  // Some things in dart_printer are not yet used
-  "lib/src/dart_backend/backend_ast_nodes.dart": const [" is never "],
-
   // Uncalled methods in SemanticSendVisitor and subclasses.
   "lib/src/resolution/semantic_visitor.dart": const [
       "The method 'error"],
   "lib/src/resolution/semantic_visitor_mixins.dart": const [
       "The class 'SuperBulkMixin'",
       "The class 'Base",
       "The method 'error",
       "The method 'visit"],
 
   // Uncalled type predicate.  Keep while related predicates are used.
@@ skipping 10 matching lines @@
   ],
 
   "lib/src/universe/universe.dart": const [
       "The method 'getterInvocationsByName' is never called.",
       "The method 'setterInvocationsByName' is never called."],
 
   "lib/src/cps_ir/": const [
     "accept", "CreateFunction",
   ],
 
-  "lib/src/dart_backend/backend_ast_to_frontend_ast.dart": const [
-    " is never "
-  ],
-
   // Useful utility functions that are not currently used.
   "lib/src/cps_ir/cps_fragment.dart": const [
     "The method 'beginLoop' is never called.",
     "The method 'continueLoop' is never called.",
     "The method 'invokeMethod' is never called.",
   ],
 };
 
 void main() {
   var uri = currentDirectory.resolve(
@@ skipping 29 matching lines @@
       if (member.isResolved) {
         compiler.reporter.reportHintMessage(
             member, MessageKind.GENERIC,
             {'text': "Helper typedef in production code '$member'."});
       }
     }
   }
   compiler.libraryLoader.lookupLibrary(helperUri).forEachLocalMember(checkLive);
   return handler.checkResults();
 }