Reenable SiteEngagementBrowserTest.All for non-Windows platforms.

chrome/test/data/webui/engagement/site_engagement_browsertest.js

Index: chrome/test/data/webui/engagement/site_engagement_browsertest.js
diff --git a/chrome/test/data/webui/engagement/site_engagement_browsertest.js b/chrome/test/data/webui/engagement/site_engagement_browsertest.js
index 0efbd08beb61486187fc988f8377b83de48886f2..96d75dd2726b6875fca045ef4535633f49e1903d 100644
--- a/chrome/test/data/webui/engagement/site_engagement_browsertest.js
+++ b/chrome/test/data/webui/engagement/site_engagement_browsertest.js
@@ -46,8 +46,13 @@ SiteEngagementBrowserTest.prototype = {
   },
 };
 
-// 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'));