Settings Chrome OS Printing Page: Fix test

Unclear how this test passed when landing:
https://chromium-review.googlesource.com/c/chromium/src/+/1994261

but it calls a method that no longer exists. Test was recently updated,
so it is likely there was an issue with auto-merge.

Bug: 967861
Change-Id: Iec8495e5253fe92dda1be5da87aa369ea86483bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003012
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Auto-Submit: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732288}

chrome/test/data/webui/settings/chromeos/cups_printer_page_tests.js

@@ -1281,7 +1281,7 @@ suite('PrintServerTests', function() {
     mojoApi_.addNetworksForTest([wifi1]);
 
     PolymerTest.clearBody();
-    settings.navigateTo(settings.routes.CUPS_PRINTERS);
+    settings.Router.getInstance().navigateTo(settings.routes.CUPS_PRINTERS);
 
     page = document.createElement('settings-cups-printers');
     document.body.appendChild(page);