Disable RenderFrameHostManagerTest.DisownOpener on Mac as it's flaky there as well.

See
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_swarming/builds/5481
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_swarming/builds/5503
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_swarming/builds/5542

BUG=291249
TBR=jdduke@chromium.org

Review URL: https://codereview.chromium.org/492303005

Cr-Commit-Position: refs/heads/master@{#291139}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291139 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/frame_host/render_frame_host_manager_browsertest.cc

@@ -412,9 +412,9 @@ IN_PROC_BROWSER_TEST_F(RenderFrameHostManagerTest,
 // Test that setting the opener to null in a window affects cross-process
 // navigations, including those to existing entries.  http://crbug.com/156669.
 // Flaky on android: http://crbug.com/397185
-// Flaky on windows: http://crbug.com/291249
+// Flaky on windows and mac: http://crbug.com/291249
 // This test also crashes under ThreadSanitizer, http://crbug.com/356758.
-#if defined(OS_ANDROID) || defined(OS_WIN) || defined(THREAD_SANITIZER)
+#if defined(OS_ANDROID) || defined(OS_WIN) || defined(THREAD_SANITIZER) || defined(OS_MACOSX)
 #define MAYBE_DisownOpener DISABLED_DisownOpener
 #else
 #define MAYBE_DisownOpener DisownOpener