Reimplement setting aria-hidden on the main app node by dispatching actions rather than assuming we can find and manipulate the node directly

src/components/structures/LoggedInView.js

@@ -327,7 +327,7 @@ const LoggedInView = React.createClass({
         }
 
         return (
-            <div className='mx_MatrixChat_wrapper'>
+            <div className='mx_MatrixChat_wrapper' aria-hidden={this.props.hideToSRUsers}>
                 { topBar }
                 <div className={bodyClasses}>
                     { SettingsStore.isFeatureEnabled("feature_tag_panel") ? <TagPanel /> : <div /> }

src/components/structures/MatrixChat.js

@@ -171,6 +171,10 @@ export default React.createClass({
             register_hs_url: null,
             register_is_url: null,
             register_id_sid: null,
+
+            // When showing Modal dialogs we need to set aria-hidden on the root app element
+            // and disable it when there are no dialogs
+            hideToSRUsers: false,
         };
         return s;
     },
@@ -608,6 +612,16 @@ export default React.createClass({
             case 'send_event':
                 this.onSendEvent(payload.room_id, payload.event);
                 break;
+            case 'aria_hide_main_app':
+                this.setState({
+                    hideToSRUsers: true,
+                });
+                break;
+            case 'aria_unhide_main_app':
+                this.setState({
+                    hideToSRUsers: false,
+                });
+                break;
         }
     },