Revert "Disable MaterialHistoryItemTest.All on Mac"

This reverts commit aec41dcb.

Reason for revert: Breaks build on Win Builder (dbg)
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win%20Builder%20%28dbg%29/50751

Original change's description:
> Disable MaterialHistoryItemTest.All on Mac
> 
> TBR=wjmaclean@chromium.org
> NOTRY=true
> 
> Bug: 874976
> Change-Id: I85a635544c5305bce8bb80ca3b2fedc50fd5a4fd
> Reviewed-on: https://chromium-review.googlesource.com/1178310
> Reviewed-by: Xida Chen <xidachen@chromium.org>
> Commit-Queue: Xida Chen <xidachen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#583730}

TBR=xidachen@chromium.org,wjmaclean@chromium.org

Change-Id: Iddba28b5f6992f94c5166192f799344065e2a274
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 874976
Reviewed-on: https://chromium-review.googlesource.com/1178501Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583735}

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

@@ -82,14 +82,7 @@ MaterialHistoryItemTest.prototype = {
   ]),
 };
 
-// https://crbug.com/874976, fails on Mac.
-GEN('#if defined(OS_MACOSX)');
-GEN('#define MAYBE_All DISABLED_All');
-GEN('#else');
-GEN('#define MAYBE_All All');
-GEN('#endif');
-
-TEST_F('MaterialHistoryItemTest', 'MAYBE_All', function() {
+TEST_F('MaterialHistoryItemTest', 'All', function() {
   mocha.run();
 });