Disable BrowserCloseManagerBrowserTest.AddBeforeUnloadDuringClosing on Mac.

BUG=713201
TBR=mkolom@yandex-team.ru, creis@chromium.org, sky@chromium.org, dgozman@chromium.org

Review-Url: https://codereview.chromium.org/2829773002
Cr-Commit-Position: refs/heads/master@{#465719}

chrome/browser/lifetime/browser_close_manager_browsertest.cc

@@ -741,8 +741,16 @@ IN_PROC_BROWSER_TEST_P(BrowserCloseManagerBrowserTest,
   EXPECT_TRUE(BrowserList::GetInstance()->empty());
 }
 
+// TODO(crbug/713201):
+// BrowserCloseManagerBrowserTest.AddBeforeUnloadDuringClosing flaky on Mac.
+#if defined(OS_MACOSX)
+#define MAYBE_AddBeforeUnloadDuringClosing DISABLED_AddBeforeUnloadDuringClosing
+#else
+#define MAYBE_AddBeforeUnloadDuringClosing AddBeforeUnloadDuringClosing
+#endif
+
 IN_PROC_BROWSER_TEST_P(BrowserCloseManagerBrowserTest,
-                       AddBeforeUnloadDuringClosing) {
+                       MAYBE_AddBeforeUnloadDuringClosing) {
   // TODO(crbug.com/250305): Currently FastUnloadController is broken.
   // And it is difficult to fix this issue without fixing that one.
   if (GetParam())