[Mac] Implement the update available notification in the wrench menu.

chrome/browser/wrench_menu_model.cc

Index: chrome/browser/wrench_menu_model.cc
diff --git a/chrome/browser/wrench_menu_model.cc b/chrome/browser/wrench_menu_model.cc
index bc5a1305de9651459fcd7e22ecde1d3decebb2bd..eb81669b98682d024038c6210eff1f6ad7866a11 100644
--- a/chrome/browser/wrench_menu_model.cc
+++ b/chrome/browser/wrench_menu_model.cc
@@ -255,7 +255,10 @@ void WrenchMenuModel::Build() {
   AddItemWithStringId(IDC_OPTIONS, IDS_OPTIONS);
 #endif
 
-  if (browser_defaults::kShowAboutMenuItem) {
+  // On Mac, there is no About item unless it is replaced with the update
+  // available notification.
+  if (browser_defaults::kShowAboutMenuItem ||
+      Singleton<UpgradeDetector>::get()->notify_upgrade()) {
     AddItem(IDC_ABOUT,
             l10n_util::GetStringFUTF16(
                 IDS_ABOUT,