Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/native_handler.dart

Index: sdk/lib/_internal/compiler/implementation/native_handler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/native_handler.dart b/sdk/lib/_internal/compiler/implementation/native_handler.dart
index f6a89b7e79930eb078a2cae80c69490d5d18d52a..d8379d886d1c3371d02d3a9a6ae535e768bfb10b 100644
--- a/sdk/lib/_internal/compiler/implementation/native_handler.dart
+++ b/sdk/lib/_internal/compiler/implementation/native_handler.dart
@@ -332,7 +332,7 @@ abstract class NativeEnqueuerBase implements NativeEnqueuer {
          !link.isEmpty;
          link = link.tail) {
       MetadataAnnotation annotation = link.head.ensureResolved(compiler);
-      var value = annotation.value;
+      var value = annotation.constant;
       if (value is! ConstructedConstant) continue;
       if (value.type is! InterfaceType) continue;
       if (!identical(value.type.element, annotationClass)) continue;
@@ -1099,19 +1099,20 @@ class NativeBehavior {
          !link.isEmpty;
          link = link.tail) {
       MetadataAnnotation annotation = link.head.ensureResolved(compiler);
-      var value = annotation.value;
-      if (value is! ConstructedConstant) continue;
-      if (value.type is! InterfaceType) continue;
-      if (!identical(value.type.element, annotationClass)) continue;
+      Constant value = annotation.constant.value;
+      if (!value.isConstructedObject) continue;
+      ConstructedConstant constructedObject = value;
+      if (constructedObject.type.element != annotationClass) continue;
 
-      var fields = value.fields;
+      List<Constant> fields = constructedObject.fields;
       // TODO(sra): Better validation of the constant.
-      if (fields.length != 1 || fields[0] is! StringConstant) {
+      if (fields.length != 1 || !fields[0].isString) {
         PartialMetadataAnnotation partial = annotation;
         compiler.internalError(annotation,
             'Annotations needs one string: ${partial.parseNode(compiler)}');
       }
-      String specString = fields[0].toDartString().slowToString();
+      StringConstant specStringConstant = fields[0];
+      String specString = specStringConstant.toDartString().slowToString();
       for (final typeString in specString.split('|')) {
         var type = _parseType(typeString, compiler, lookup, annotation);
         if (types == null) types = [];