Revert of Disable MaterialHistoryBrowserTest.HistoryListTest since

chrome/test/data/webui/md_history/md_history_browsertest.js

Index: chrome/test/data/webui/md_history/md_history_browsertest.js
diff --git a/chrome/test/data/webui/md_history/md_history_browsertest.js b/chrome/test/data/webui/md_history/md_history_browsertest.js
index c7bf5f3dcd1cbffc33e38215ca0d90326e63ab62..61777b5c0695f11a8334f024f6d30224209b204c 100644
--- a/chrome/test/data/webui/md_history/md_history_browsertest.js
+++ b/chrome/test/data/webui/md_history/md_history_browsertest.js
@@ -86,8 +86,7 @@
   mocha.run();
 });
 
-// Flaky on chromeos, http://crbug.com/640862
-TEST_F('MaterialHistoryBrowserTest', 'DISABLED_HistoryListTest', function() {
+TEST_F('MaterialHistoryBrowserTest', 'HistoryListTest', function() {
   md_history.history_list_test.registerTests();
   mocha.run();
 });