media: disable RecordSingleVisitOnSameOrigin on Mac

This test is already disabled as flaky on Windows & Linux; it appears to flakily
time out on Mac (quite often actually) as well.

Bug: 1014229, 1028239
Change-Id: I278543f670e5723ecb0428d09863367bbf8c772e
Tbr: thestig@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946824Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720562}

chrome/browser/media/media_engagement_browsertest.cc

@@ -517,7 +517,7 @@ IN_PROC_BROWSER_TEST_F(MediaEngagementBrowserTest, RecordVisitOnBrowserClose) {
   ExpectScores(1, 0, 1, 0);
 }
 
-#if defined(OS_WIN) || defined(OS_LINUX)
+#if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_MACOSX)
 // Flaky timeout. https://crbug.com/1014229
 #define MAYBE_RecordSingleVisitOnSameOrigin \
   DISABLED_RecordSingleVisitOnSameOrigin