Start building message_center on Mac.

ui/message_center/message_center_util.cc

Index: ui/message_center/message_center_util.cc
diff --git a/ui/message_center/message_center_util.cc b/ui/message_center/message_center_util.cc
index 3b1f1e7e01175179bdd843d31eb7a32b6eb23979..de2a06f5b28dee0c01d8f006012ed170c979ba46 100644
--- a/ui/message_center/message_center_util.cc
+++ b/ui/message_center/message_center_util.cc
@@ -13,7 +13,12 @@ namespace message_center {
 // when a time period in Canary indicates the new notifications are acceptable
 // for default behavior.
 bool IsRichNotificationEnabled() {
+#if defined(OS_MACOSX)
+  return CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableRichNotifications);
+#else
   return true;
+#endif
 }
 
 }  // namespace message_center