Disable test CrElementsToggleTest.All on windows

Looks like it's been failing on the win10 bot for some time now.

Bug: 770574
TBR: dpapad@chromium.org
Change-Id: I6d9cc7137de216535b3a2c0bc45bdad2068a4ce2
Reviewed-on: https://chromium-review.googlesource.com/695704Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505744}

chrome/test/data/webui/cr_elements/cr_elements_browsertest.js

@@ -315,6 +315,14 @@ CrElementsToggleTest.prototype = {
   ]),
 };
 
-TEST_F('CrElementsToggleTest', 'All', function() {
+// Times out on Windows 10.
+// https://crbug.com/770574.
+GEN('#if defined(OS_WIN)');
+GEN('#define MAYBE_All DISABLED_All');
+GEN('#else');
+GEN('#define MAYBE_All All');
+GEN('#endif');
+
+TEST_F('CrElementsToggleTest', 'MAYBE_All', function() {
   mocha.run();
 });