Make a viewState a state in gr-editor-view

Release-Notes: skip
Change-Id: I8d678fa7227eb016b91e76fa9e13c61b78f966b0
(cherry picked from commit 22540fd3dac0c4f897dea18d8c8c606361b36b67)
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 18ce3d1..8bed2a2 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';
@@ -57,8 +57,7 @@
    * @event show-alert
    */
 
-  @property({type: Object})
-  viewState?: EditViewState;
+  @state() viewState?: EditViewState;
 
   // private but used in test
   @state() change?: ParsedChangeInfo;