EulaScreen: Return focus to link after quiting System security settings.

Bug: 1049959
Change-Id: Ic0ff0f33c61ad479fca631a6e98bc88aa84b674a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216213Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Roman Aleksandrov <raleksandrov@google.com>
Cr-Commit-Position: refs/heads/master@{#772186}

chrome/browser/resources/chromeos/login/oobe_eula.js

@@ -206,6 +206,7 @@ Polymer({
     this.$.installationSettingsDialog.hidden = true;
     this.$.eulaDialog.hidden = false;
     this.$.eulaDialog.show();
+    this.$.installationSettings.focus();
   },
 
   /**