Optimize DDC private library files.

pkg/dev_compiler/lib/src/compiler/js_interop.dart

 // Copyright (c) 2015, 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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/dart/element/element.dart';
 
 import 'element_helpers.dart';
 
@@ skipping 52 matching lines @@
 
 bool isJsName(DartObjectImpl value) =>
     _isBuiltinAnnotation(value, '_js_helper', 'JSName');
 
 bool isJsPeerInterface(DartObjectImpl value) =>
     _isBuiltinAnnotation(value, '_js_helper', 'JsPeerInterface');
 
 bool isNativeAnnotation(DartObjectImpl value) =>
     _isBuiltinAnnotation(value, '_js_helper', 'Native');
 
+bool isNotNullAnnotation(DartObjectImpl value) =>
+    _isBuiltinAnnotation(value, '_js_helper', 'NotNull');
+
+bool isNullCheckAnnotation(DartObjectImpl value) =>
+    _isBuiltinAnnotation(value, '_js_helper', 'NullCheck');
+
 /// Returns the name value of the `JSExportName` annotation (when compiling
 /// the SDK), or `null` if there's none. This is used to control the name
 /// under which functions are compiled and exported.
 String getJSExportName(Element e) {
   if (!e.source.isInSystemLibrary) return null;
 
   e = e is PropertyAccessorElement && e.isSynthetic ? e.variable : e;
   return getAnnotationName(e, isJSExportNameAnnotation);
 }