Cef右鍵菜單顯示DevTools失敗

我在cef 3.3239提供的CefSimple中想加一個 Show DevTools的右鍵菜單選項，但是調(diào)試發(fā)現(xiàn)一直沒進(jìn)來OnBeforeContextMenu這個函數(shù)。代碼如下：

// 1. SimpleHandler添加CefContextMenuHandler繼承
class SimpleHandler : public ...
                      public public CefContextMenuHandler { /**/ }


// 2. 重寫CefContextMenuHandler和OnContextMenuCommand事件回調(diào)

// Cef源碼注釋："Called before a context menu is displayed..."
void SimpleHandler::OnBeforeContextMenu(CefRefPtr<CefBrowser> browser, 
        CefRefPtr<CefFrame> frame,
        CefRefPtr<CefContextMenuParams> params,
        CefRefPtr<CefMenuModel> model) {
    CEF_REQUIRE_UI_THREAD();
    if ((params->GetTypeFlags() & (CM_TYPEFLAG_PAGE | CM_TYPEFLAG_FRAME)) != 0) {
        if (model->GetCount() > 0)
            model->AddSeparator();

        model->AddItem(DEV_TOOLS_ID, "&Show DevTools");    // 添加一個右鍵菜單項
    }
}

// Cef源碼注釋：Called to execute a command selected from the context menu
bool SimpleHandler::OnContextMenuCommand(CefRefPtr<CefBrowser> browser,
        CefRefPtr<CefFrame> frame,
        CefRefPtr<CefContextMenuParams> params,
        int command_id,
        EventFlags event_flags) {
    CEF_REQUIRE_UI_THREAD();
    switch (command_id)
    {
    case DEV_TOOLS_ID:
        ShowDevTools(browser);    // 顯示DevTools
        break;
    default:
        break;
    }
    
    return true;
}

void SimpleHandler::ShowDevTools(CefRefPtr<CefBrowser> browser)
{
    CefWindowInfo win_info;
    CefRefPtr<CefClient> client;
    CefBrowserSettings settings;

    browser->GetHost()->ShowDevTools(win_info, client, settings, CefPoint());
}

但是我運(yùn)行程序之后，發(fā)現(xiàn)右鍵菜單沒有添加上我要的DevToos，斷點(diǎn)設(shè)置在OnBeforeContextMenu和OnContextMenuCommand發(fā)現(xiàn)都沒進(jìn)來。
請問是我實(shí)現(xiàn)的方式缺少調(diào)用某些操作了嗎？