Optimize DDC private library files.

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

Index: pkg/dev_compiler/lib/src/compiler/js_interop.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/js_interop.dart b/pkg/dev_compiler/lib/src/compiler/js_interop.dart
index 0883e414a2d10446eb16cea2369c2ee2f9590193..46f27ad7689d985ddb7398793afcc3cdaf6656fc 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_interop.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_interop.dart
@@ -70,6 +70,12 @@ bool isJsPeerInterface(DartObjectImpl value) =>
 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.