dart2js cps: Backward redundant null check removal

pkg/compiler/lib/src/js_backend/codegen/task.dart

 // Copyright (c) 2014, 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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 import 'unsugar.dart';
@@ skipping 202 matching lines @@
       applyCpsPass(new GVN(compiler, typeSystem), cpsFunction);
       applyCpsPass(new UpdateRefinements(typeSystem), cpsFunction);
       applyCpsPass(new BoundsChecker(typeSystem, compiler.world), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
       applyCpsPass(new ScalarReplacer(compiler), cpsFunction);
       applyCpsPass(new MutableVariableEliminator(), cpsFunction);
       applyCpsPass(new RedundantJoinEliminator(), cpsFunction);
       applyCpsPass(new RedundantPhiEliminator(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
       applyCpsPass(new OptimizeInterceptors(backend), cpsFunction);
+      applyCpsPass(new BackwardNullCheckRemover(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
     });
     return cpsFunction;
   }
 
   tree_ir.FunctionDefinition compileToTreeIr(cps.FunctionDefinition cpsNode) {
     applyCpsPass(new Finalize(backend), cpsNode);
     tree_builder.Builder builder = new tree_builder.Builder(
         reporter.internalError);
     tree_ir.FunctionDefinition treeNode =
@@ skipping 51 matching lines @@
         treeOptimizationTask]
       ..addAll(fallbackCompiler.tasks);
   }
 
   js.Node attachPosition(js.Node node, AstElement element) {
     return node.withSourceInformation(
         sourceInformationFactory.createBuilderForContext(element)
             .buildDeclaration(element));
   }
 }