[Media Router WebUI] Handle on dialog load focus on Mac.

chrome/test/data/webui/media_router/media_router_elements_browsertest.js

Index: chrome/test/data/webui/media_router/media_router_elements_browsertest.js
diff --git a/chrome/test/data/webui/media_router/media_router_elements_browsertest.js b/chrome/test/data/webui/media_router/media_router_elements_browsertest.js
index c2afb9d762f88dc713dd9b45b3ebc58a5b4de70e..3b9a65d5341d543ea4ff049e8600873850ea6c50 100644
--- a/chrome/test/data/webui/media_router/media_router_elements_browsertest.js
+++ b/chrome/test/data/webui/media_router/media_router_elements_browsertest.js
@@ -73,6 +73,12 @@ MediaRouterElementsBrowserTest.prototype = {
     // AX_ARIA_08: http://crbug.com/591552
     this.accessibilityAuditConfig.ignoreSelectors(
         'requiredOwnedAriaRoleMissing', requiredOwnedAriaRoleMissingSelectors);
+
+    // This element is used as a focus placeholder on dialog open, then
+    // deleted. The user will be unable to tab to it. Remove when there is a
+    // long term fix.
+    this.accessibilityAuditConfig.ignoreSelectors(
+       'focusableElementNotVisibleAndNotAriaHidden', '#focus-placeholder');
   },
 };