Add browser_test to test allow sign-in behavior during sync setup

During sync setup the toggle which controls chrome sign in should be
disabled in an on state, signifying to the user that this control cannot
be changed during sync setup.

Previously this behaviour was tested manually. This CL extends the
existing browser_test to confirm this behaviour.

Bug: 1043948
Change-Id: Idd54b3ad0fd83e70b7ba356aa11dae66fdb27e52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2088372Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Theodore Olsauskas-Warren <sauski@google.com>
Cr-Commit-Position: refs/heads/master@{#747064}

chrome/test/data/webui/settings/personalization_options_test.js

@@ -101,6 +101,12 @@ cr.define('settings_personalization_options', function() {
         testElement.showRestartToast_ = false;
         assertFalse(testElement.$.toast.open);
 
+        // When the user is part way through sync setup, the toggle should be
+        // disabled in an on state.
+        testElement.syncStatus = {firstSetupInProgress: true};
+        assertTrue(toggle.disabled);
+        assertTrue(toggle.checked);
+
         testElement.syncStatus = {signedIn: true};
         // When the user is signed in, clicking the toggle should open the
         // sign-out dialog.