dart2js cps_ir: avoid world.fieldNeverChanges()

pkg/compiler/lib/src/cps_ir/share_final_fields.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.
 
 library dart2js.cps_ir.share_final_fields;
 
 import 'optimizers.dart';
 import 'cps_ir_nodes.dart';
 import 'loop_hierarchy.dart';
 import '../elements/elements.dart';
@@ skipping 129 matching lines @@
 
     pushAction(() {
         var map = fieldValues[field];
         assert(map[receiver] == primitive);
         map.remove(receiver);
       });
     return next;
   }
 
   bool shouldShareField(FieldElement field) {
-    return backend.compiler.world.fieldNeverChanges(field);
+    // TODO(24781): This query is incorrect for fields assigned only via
+    //
+    //     super.field = ...
+    //
+    // return backend.compiler.world.fieldNeverChanges(field);
+
+    // Native fields are getters with side effects (e.g. layout).
+    if (backend.isNative(field)) return false;
+    return field.isFinal || field.isConst;
   }
 
   /// Returns the the innermost loop that effectively encloses both
   /// c1 and c2 (or `null` if there is no such loop).
   Continuation lowestCommonAncestor(Continuation c1, Continuation c2) {
     int d1 = getDepth(c1), d2 = getDepth(c2);
     while (c1 != c2) {
       if (d1 <= d2) {
         c2 = loopHierarchy.getEnclosingLoop(c2);
         d2 = getDepth(c2);
       } else {
         c1 = loopHierarchy.getEnclosingLoop(c1);
         d1 = getDepth(c1);
       }
     }
     return c1;
   }
 
   int getDepth(Continuation loop) {
     if (loop == null) return -1;
     return loopHierarchy.loopDepth[loop];
   }
 }