[App Management] Add missing polymer binding.

Add missing polymer binding.

Bug: 1008121
Change-Id: I881dbec7fa9571c70eb571db9b19b2c46f5c7a02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911069Reviewed-by: Alan Cutter <alancutter@chromium.org>
Commit-Queue: Jeevan Shikaram <jshikaram@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714768}

chrome/browser/resources/settings/chromeos/os_apps_page/os_apps_page.html

@@ -77,7 +77,7 @@
       </template>
     </div>
     <!-- APP MANAGEMENT -->
-    <template is="dom-if" if="showAppManagement">
+    <template is="dom-if" if="[[showAppManagement]]">
       <template is="dom-if" route-path="/app-management" no-search>
         <settings-subpage
             page-title="$i18n{appManagementTitle}"