Reenable SiteEngagementBrowserTest.All for non-Windows platforms.

chrome/test/data/webui/engagement/site_engagement_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 Test suite for the Site Engagement WebUI.
  */
 var ROOT_PATH = '../../../../../';
 var EXAMPLE_URL_1 = 'http://example.com/';
 var EXAMPLE_URL_2 = 'http://shmlexample.com/';
@@ skipping 28 matching lines @@
 
   /** @override */
   setUp: function() {
     testing.Test.prototype.setUp.call(this);
     suiteSetup(function() {
       return whenPageIsPopulatedForTest();
     });
   },
 };
 
-// TODO(crbug.com/734716): This test is flaky.
-TEST_F('SiteEngagementBrowserTest', 'DISABLED_All', function() {
+// This test is flaky on Windows. See https://crbug.com/734716.
+GEN('#if defined(OS_WIN)');
+GEN('#define MAYBE_All DISABLED_All');
+GEN('#else');
+GEN('#define MAYBE_All All');
+GEN('#endif');
+TEST_F('SiteEngagementBrowserTest', 'MAYBE_All', function() {
   test('check engagement values are loaded', function() {
     var originCells =
         Array.from(document.getElementsByClassName('origin-cell'));
     assertDeepEquals(
         [EXAMPLE_URL_1, EXAMPLE_URL_2], originCells.map(x => x.textContent));
   });
 
   test('scores rounded to 2 decimal places', function() {
     var scoreInputs =
         Array.from(document.getElementsByClassName('base-score-input'));
     assertDeepEquals(['10', '3.14'], scoreInputs.map(x => x.value));
     var bonusScoreCells =
         Array.from(document.getElementsByClassName('bonus-score-cell'));
     assertDeepEquals(['0', '0'], bonusScoreCells.map(x => x.textContent));
     var totalScoreCells =
         Array.from(document.getElementsByClassName('total-score-cell'));
     assertDeepEquals(['10', '3.14'], totalScoreCells.map(x => x.textContent));
   });
   mocha.run();
 });