[serial] Enable serialPorts settings route

This is a follow-up to r707007 which enables the route for
chrome://settings/content/serialPorts. Otherwise the "Serial ports"
option is visible but clicking it does nothing.

Bug: 967863
Change-Id: I53a04345cb63fe5045e0de2a475dc7b61945a676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872738
Auto-Submit: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Dan Beam <dbeam@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708067}

chrome/browser/resources/settings/route.js

@@ -347,10 +347,7 @@ cr.define('settings', function() {
           r.SITE_SETTINGS.createChild('unsandboxedPlugins');
       r.SITE_SETTINGS_MIDI_DEVICES = r.SITE_SETTINGS.createChild('midiDevices');
       r.SITE_SETTINGS_USB_DEVICES = r.SITE_SETTINGS.createChild('usbDevices');
-      if (loadTimeData.getBoolean('enableExperimentalWebPlatformFeatures')) {
-        r.SITE_SETTINGS_SERIAL_PORTS =
-            r.SITE_SETTINGS.createChild('serialPorts');
-      }
+      r.SITE_SETTINGS_SERIAL_PORTS = r.SITE_SETTINGS.createChild('serialPorts');
       r.SITE_SETTINGS_ZOOM_LEVELS = r.SITE_SETTINGS.createChild('zoomLevels');
       r.SITE_SETTINGS_PDF_DOCUMENTS =
           r.SITE_SETTINGS.createChild('pdfDocuments');