Add setting to isolate zoom changes by default.

chrome/browser/ui/webui/options/chromeos/guest_mode_options_browsertest.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 GEN_INCLUDE(['../options_browsertest_base.js']);
 GEN('#include "chrome/browser/ui/webui/options/chromeos/' +
     'guest_mode_options_browsertest.h"');
 
 /**
  * TestFixture for guest mode options WebUI testing.
@@ skipping 52 matching lines @@
   expectTrue($('timezone-value-select').disabled);
   expectFalse($('resolve-timezone-by-geolocation').disabled);
   expectFalse($('use-24hour-clock').disabled);
 
   // Privacy section.
   expectTrue(this.getControlForPref('search.suggest_enabled').disabled);
   expectTrue($('networkPredictionOptions').disabled);
 
   // Web content section.
   expectTrue($('defaultZoomFactor').disabled);
+  expectTrue($('defaultZoomScope').disabled);
 
   // Downloads section.
   expectTrue(this.getControlForPref('gdata.disabled').disabled);
 
   // Content settings overlay.
   expectTrue(this.getControlForPref('settings.privacy.drm_enabled').disabled);
   expectTrue($('protected-content-exceptions').disabled);
 });