fix #27643, failed to virtualize fields if an abstract one is mixed in

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

Index: pkg/dev_compiler/lib/src/compiler/js_field_storage.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/js_field_storage.dart b/pkg/dev_compiler/lib/src/compiler/js_field_storage.dart
index decef3b8a894079cfeb42230d98dde66e47e9e2f..13d598024f4ee28b2483c0a2f7d19500d1956f2f 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_field_storage.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_field_storage.dart
@@ -30,10 +30,6 @@ PropertyOverrideResult checkForPropertyOverride(
     var setter = superprop.setter;
     bool hasSetter = setter != null && !setter.isAbstract;
     if (hasSetter) foundSetter = true;
-
-    // Stop if this is an abstract getter/setter
-    // TODO(jmesserly): why were we doing this?
-    if (!hasGetter && !hasSetter) break;
   }
 
   return new PropertyOverrideResult(foundGetter, foundSetter);