Cleanup universe to not have backend related things.

tests/compiler/dart2js/compiler_helper.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.
 // Test constant folding.
 
 library compiler_helper;
 
 import "dart:uri";
 
 import "../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart"
@@ skipping 29 matching lines @@
   compiler.backend.enqueueHelpers(compiler.enqueuer.resolution);
   compiler.processQueue(compiler.enqueuer.resolution, element);
   var context = new js.JavaScriptItemCompilationContext();
   leg.ResolutionWorkItem resolutionWork =
       new leg.ResolutionWorkItem(element, context);
   resolutionWork.run(compiler, compiler.enqueuer.resolution);
   leg.CodegenWorkItem work =
       new leg.CodegenWorkItem(element, resolutionWork.resolutionTree, context);
   compiler.phase = Compiler.PHASE_COMPILING;
   work.run(compiler, compiler.enqueuer.codegen);
-  return compiler.enqueuer.codegen.assembleCode(element);
+  js.JavaScriptBackend backend = compiler.backend;
+  return backend.assembleCode(element);
 }
 
 MockCompiler compilerFor(String code, Uri uri,
                          {bool analyzeAll: false,
                           String coreSource: DEFAULT_CORELIB}) {
   MockCompiler compiler = new MockCompiler(
       analyzeAll: analyzeAll, coreSource: coreSource);
   compiler.sourceFiles[uri.toString()] = new SourceFile(uri.toString(), code);
   return compiler;
 }
@@ skipping 72 matching lines @@
   final xRe = new RegExp('\\bx\\b');
   regexp = regexp.replaceAll(xRe, '(?:$anyIdentifier)');
   final spaceRe = new RegExp('\\s+');
   regexp = regexp.replaceAll(spaceRe, '(?:\\s*)');
   if (shouldMatch) {
     Expect.isTrue(new RegExp(regexp).hasMatch(generated));
   } else {
     Expect.isFalse(new RegExp(regexp).hasMatch(generated));
   }
 }