Add policy to use system default printer

chrome/test/data/webui/print_preview/print_preview_ui_browsertest.js

 // Copyright 2017 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.
 
 /** @fileoverview Runs the Print Preview tests. */
 
 var ROOT_PATH = '../../../../../';
 
 /**
  * @constructor
@@ skipping 96 matching lines @@
 // Disable accessibility errors for some tests.
 [
   'AdvancedSettings1Option',
   'AdvancedSettings2Options',
 ].forEach(function(testName) {
   TEST_F('PrintPreviewUIBrowserTest', testName, function() {
     this.accessibilityIssuesAreErrors = false;
     mocha.grep(new RegExp(testName + '\\b')).run();
   });
 });
+
+TEST_F('PrintPreviewUIBrowserTest', 'SystemDefaultPrinterPolicy', function() {
+  loadTimeData.overrideValues({useSystemDefaultPrinter: true});

[dpapad, 2017/06/19 17:43:37]

Can we not do this inside SystemDefaultPrinterPolicy test instead? Then we can
just add 'SystemDefaultPrinterPolicy' to the array above.

Also does this test make sense on ChromeOS? It seems that it should only run on
non-ChromeOS code.

[rbpotter, 2017/06/19 23:10:49]

It doesn't work inside the test as print preview has already been
created at that point (in setup()). The policy is only checked at
creation so it has to be set before then.

Changed it to only run on non-ChromeOS.

+  mocha.grep(new RegExp('SystemDefaultPrinterPolicy' + '\\b')).run();
+});