Revert "Enforce use of the forEachInstanceField ordering for constructed constants."

pkg/compiler/lib/src/js_backend/constant_emitter.dart

Index: pkg/compiler/lib/src/js_backend/constant_emitter.dart
diff --git a/pkg/compiler/lib/src/js_backend/constant_emitter.dart b/pkg/compiler/lib/src/js_backend/constant_emitter.dart
index 85f06e8d48a13c330371c5ead7cbecad11c4a2c0..e88d927fdb8f4c819941282cc2f2106576f21723 100644
--- a/pkg/compiler/lib/src/js_backend/constant_emitter.dart
+++ b/pkg/compiler/lib/src/js_backend/constant_emitter.dart
@@ -285,7 +285,7 @@ class ConstantEmitter implements ConstantValueVisitor<jsAst.Expression, Null> {
 
   @override
   jsAst.Expression visitConstructed(ConstructedConstantValue constant, [_]) {
-    ClassElement element = constant.type.element;
+    Element element = constant.type.element;
     if (backend.isForeign(element) && element.name == 'JS_CONST') {
       StringConstantValue str = constant.fields.values.single;
       String value = str.primitiveValue.slowToString();
@@ -293,10 +293,9 @@ class ConstantEmitter implements ConstantValueVisitor<jsAst.Expression, Null> {
     }
     jsAst.Expression constructor =
         backend.emitter.constructorAccess(constant.type.element);
-    List<jsAst.Expression> fields = <jsAst.Expression>[];
-    element.forEachInstanceField((_, FieldElement field) {
-      fields.add(constantReferenceGenerator(constant.fields[field]));
-    });
+    List<jsAst.Expression> fields = constant.fields.values
+        .map(constantReferenceGenerator)
+        .toList(growable: false);
     jsAst.New instantiation = new jsAst.New(constructor, fields);
     return maybeAddTypeArguments(constant.type, instantiation);
   }