See:

https://chromium-review.googlesource.com/c/chromium/src/+/687988/6/chrome/renderer/extensions/automation_internal_custom_bindings.cc

It's formatting it like this:

void AutomationInternalCustomBindings::OnMessageReceived(
    const IPC::Message& message){
    IPC_BEGIN_MESSAGE_MAP(AutomationInternalCustomBindings, message)
        IPC_MESSAGE_HANDLER(ExtensionMsg_AccessibilityEvent,
                            OnAccessibilityEvent)
            IPC_MESSAGE_HANDLER(ExtensionMsg_AccessibilityLocationChange,
                                OnAccessibilityLocationChange)
                IPC_END_MESSAGE_MAP()}