Disable SitePerProcessBrowserTest.ScrollBubblingFromOOPIFWithBodyOverflowHidden on Mac

Bug: 863971
Change-Id: I7401eaf54693c83145b5a67c17da1ca1e69c9184
Tbr: nasko@chromium.org
NoTry: True
Reviewed-on: https://chromium-review.googlesource.com/1138376Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575337}

content/browser/site_per_process_browsertest.cc

@@ -1763,8 +1763,9 @@ IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest,
   scroll_observer->Wait();
 }
 
-#if defined(OS_CHROMEOS)
+#if defined(OS_CHROMEOS) || defined(OS_MACOSX)
 // Flaky: https://crbug.com/836200.
+// Flaky timeouts on Mac: https://crbug.com/863971.
 #define MAYBE_ScrollBubblingFromOOPIFWithBodyOverflowHidden \
   DISABLED_ScrollBubblingFromOOPIFWithBodyOverflowHidden
 #else