Make a viewState a state in gr-editor-view

Release-Notes: skip
Change-Id: I8d678fa7227eb016b91e76fa9e13c61b78f966b0
diff --git a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
index 12a20c1..12b19c7 100644
--- a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
+++ b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
@@ -26,7 +26,7 @@
 import {Modifier} from '../../../utils/dom-util';
 import {sharedStyles} from '../../../styles/shared-styles';
 import {LitElement, PropertyValues, html, css, nothing} from 'lit';
-import {customElement, property, state} from 'lit/decorators.js';
+import {customElement, state} from 'lit/decorators.js';
 import {subscribe} from '../../lit/subscription-controller';
 import {resolve} from '../../../models/dependency';
 import {changeModelToken} from '../../../models/change/change-model';
@@ -63,8 +63,7 @@
    * @event show-alert
    */
 
-  @property({type: Object})
-  viewState?: ChangeViewState;
+  @state() viewState?: ChangeViewState;
 
   // private but used in test
   @state() change?: ParsedChangeInfo;