Re-disable HistorySupervisedUserTest on Mac

The test was mistakely disabled on all platforms but Mac. However, it
should be disabled in the exactly opposite way.

Tbr: dpapad@chromium.org
Bug: 1028129
Change-Id: Ie54a98fe84db3be5a8989bd9cf1553591c69f067
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1933597Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718770}

chrome/test/data/webui/history/history_browsertest.js

@@ -210,7 +210,7 @@ HistorySupervisedUserTest.prototype = {
   ]),
 };
 
-GEN('#if !defined(OS_MACOSX)');
+GEN('#if defined(OS_MACOSX)');
 GEN('#define MAYBE_AllTest DISABLED_AllTest');
 GEN('#else');
 GEN('#define MAYBE_AllTest AllTest');