Add UMA to track app launcher discoverability.

chrome/browser/ui/app_list/app_list_service_mac.mm

Index: chrome/browser/ui/app_list/app_list_service_mac.mm
diff --git a/chrome/browser/ui/app_list/app_list_service_mac.mm b/chrome/browser/ui/app_list/app_list_service_mac.mm
index fd5986eef68a1da2c5b6a9756a054289967e55f7..8ee88d126804a0174846dbf66cb348a4191fd213 100644
--- a/chrome/browser/ui/app_list/app_list_service_mac.mm
+++ b/chrome/browser/ui/app_list/app_list_service_mac.mm
@@ -442,8 +442,9 @@ bool AppListServiceMac::IsAppListVisible() const {
       ![animation_controller_ isClosing];
 }
 
-void AppListServiceMac::EnableAppList(Profile* initial_profile) {
-  AppListServiceImpl::EnableAppList(initial_profile);
+void AppListServiceMac::EnableAppList(Profile* initial_profile,
+                                      AppListEnableSource enable_source) {
+  AppListServiceImpl::EnableAppList(initial_profile, enable_source);
   AppController* controller = [NSApp delegate];
   [controller initAppShimMenuController];
 }