Settings WebUI: Restore focus when exiting security keys subpage.

Bug: 947926
Change-Id: I14d96dc424c6edc7073d7d8135c67ac42fd7ff92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1546062Reviewed-by: Adam Langley <agl@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646457}

chrome/browser/resources/settings/privacy_page/privacy_page.js

@@ -173,6 +173,12 @@ Polymer({
               settings.routes.SITE_SETTINGS_SITE_DATA.path,
               '#site-data-trigger .subpage-arrow button');
         }
+
+        if (settings.routes.SECURITY_KEYS) {
+          map.set(
+              settings.routes.SECURITY_KEYS.path,
+              '#security-keys-subpage-trigger');
+        }
         return map;
       },
     },