Disable crostini backup restore when disabled by policy

Ensure route for /crostini/exportImport is not added
when backup and restore is disabled by policy.

Bug: 1003944
Change-Id: I9c88d038e928948e5bea2363592612097bf42d9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1809122Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Auto-Submit: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697423}

chrome/browser/resources/settings/route.js

@@ -465,8 +465,11 @@ cr.define('settings', function() {
         loadTimeData.getBoolean('showCrostini')) {
       r.CROSTINI = r.BASIC.createSection('/crostini', 'crostini');
       r.CROSTINI_DETAILS = r.CROSTINI.createChild('/crostini/details');
-      r.CROSTINI_EXPORT_IMPORT =
-          r.CROSTINI_DETAILS.createChild('/crostini/exportImport');
+      if (loadTimeData.valueExists('showCrostiniExportImport') &&
+          loadTimeData.getBoolean('showCrostiniExportImport')) {
+        r.CROSTINI_EXPORT_IMPORT =
+            r.CROSTINI_DETAILS.createChild('/crostini/exportImport');
+      }
       r.CROSTINI_SHARED_PATHS =
           r.CROSTINI_DETAILS.createChild('/crostini/sharedPaths');
       r.CROSTINI_SHARED_USB_DEVICES =