Disable CrExtensionsPackDialogTest.PackSuccess on Mac

Bug: 877109
Change-Id: I77918382df9e5ef5c14f3f55d2581bc58c5ccb3b
Reviewed-on: https://chromium-review.googlesource.com/1187656Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585923}

chrome/test/data/webui/extensions/cr_extensions_browsertest.js

@@ -518,7 +518,9 @@ TEST_F('CrExtensionsPackDialogTest', 'Interaction', function() {
 
 // Disabling on Windows due to flaky timeout on some build bots.
 // http://crbug.com/832885
-GEN('#if defined(OS_WIN)');
+// Temporarily disabling on Mac due to flaky dialog visibility failure.
+// http://crbug.com/877109
+GEN('#if defined(OS_WIN) || defined(OS_MACOSX)');
 GEN('#define MAYBE_PackSuccess DISABLED_PackSuccess');
 GEN('#else');
 GEN('#define MAYBE_PackSuccess PackSuccess');