dart2js cps: Backward redundant null check removal

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

Index: pkg/compiler/lib/src/js_backend/codegen/task.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/task.dart b/pkg/compiler/lib/src/js_backend/codegen/task.dart
index 78f61cb1bad41b528b5bc101473c4eeb6b551b65..0e9f044b46cbf31140cb17963c0c6bdf870565b7 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/task.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/task.dart
@@ -220,6 +220,7 @@ class CpsFunctionCompiler implements FunctionCompiler {
       applyCpsPass(new RedundantPhiEliminator(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
       applyCpsPass(new OptimizeInterceptors(backend), cpsFunction);
+      applyCpsPass(new BackwardNullCheckRemover(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
     });
     return cpsFunction;