[App Management] Fix App Info dialog.

This CL checks that the apps have been loaded before checking if
an app exists in the apps list. It also handles a race condition
where the dom-switch element's onRouteChanged is called before
the dom-switch has a child loaded.

Bug: 1014919
Change-Id: Id0712b74b006580bfbed2c701a3e61320094a036
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1889274
Commit-Queue: Jeevan Shikaram <jshikaram@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710756}

chrome/browser/resources/settings/chromeos/os_apps_page/app_management_page/app_permission_view.js

@@ -44,8 +44,9 @@ Polymer({
     }
 
     const appId = settings.getQueryParameters().get('id');
+    const apps = this.getState().apps;
 
-    if (!this.getState().apps[appId]) {
+    if (!apps[appId] && Object.entries(apps).length !== 0) {
       // TODO(crbug.com/1010398): this call does not open the main page.
       app_management.util.openMainPage();
       return;

chrome/browser/resources/settings/chromeos/os_apps_page/app_management_page/dom_switch.js

@@ -109,6 +109,10 @@ Polymer({
     }
 
     if (newRouteId === null) {
+      if (this.selectedChild_ === null) {
+        return;
+      }
+
       this.parentNode.removeChild(this.selectedChild_);
       this.selectedChild_ = null;
       return;