Add mac_window_server_killers to browser_tests data on Mac.

TBR=ellyjones@chromium.org,liaoyuke@chromium.org

Bug: 828031
Change-Id: Ie98ee83cee2d4c98c29a2ac1290728da5b87c4a7
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/1028482Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553626}

chrome/test/BUILD.gn

@@ -1883,6 +1883,8 @@ test("browser_tests") {
         "../browser/process_singleton_browsertest.cc",
       ]
 
+      data += [ "mac_window_server_killers.browser_tests.filter" ]
+
       if (safe_browsing_mode == 1) {
         sources -= [
           # single-process mode hangs on Mac sometimes because of multiple UI