chrome: mac: Add Alerts helper app (fixes #3181)

Some Chromium code cleanup will follow in
https://chromium-review.googlesource.com/c/chromium/src/+/4456752

cmake/cef_variables.cmake.in

@@ -359,6 +359,7 @@ if(OS_MAC)
   # Format is "<name suffix>:<target suffix>:<plist suffix>".
   set(CEF_HELPER_APP_SUFFIXES
     "::"
+    " (Alerts):_alerts:.alerts"
     " (GPU):_gpu:.gpu"
     " (Plugin):_plugin:.plugin"
     " (Renderer):_renderer:.renderer"