为什么要覆盖WebBrowser的PreProcessMessage和WndProc，希望捕获鼠标点击无效？

Question

我编写了这个垃圾：

using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    class SmartWebBrowser : WebBrowser
    {
        private const int WM_LBUTTONDOWN = 0x0201;
        private const int WM_LBUTTONUP = 0x0202;
        private const int WM_LBUTTONDBLCLK = 0x0203;

        private const int WM_RBUTTONDOWN = 0x0204;
        private const int WM_RBUTTONUP = 0x0205;
        private const int WM_RBUTTONDBLCLK = 0x0206;

        private const int WM_MBUTTONUP = 0x0208;
        private const int WM_MBUTTONDOWN = 0x0209;

        public override bool PreProcessMessage(ref Message msg)
        {
            bool allow_propagation = true;

            switch (msg.Msg)
            {
                case WM_LBUTTONDOWN:
                case WM_LBUTTONUP:
                case WM_LBUTTONDBLCLK:
                case WM_RBUTTONDOWN:
                case WM_RBUTTONUP:
                case WM_RBUTTONDBLCLK:
                case WM_MBUTTONUP:
                case WM_MBUTTONDOWN:
                    allow_propagation = false; //breakpoint here
                    break;
            }

            if (allow_propagation)
                return base.PreProcessMessage(ref msg);
            else
                return false;
        }

        protected override void WndProc(ref Message msg)
        {
            bool allow_propagation = true;

            switch (msg.Msg)
            {
                case WM_LBUTTONDOWN:
                case WM_LBUTTONUP:
                case WM_LBUTTONDBLCLK:
                case WM_RBUTTONDOWN:
                case WM_RBUTTONUP:
                case WM_RBUTTONDBLCLK:
                case WM_MBUTTONUP:
                case WM_MBUTTONDOWN:
                    allow_propagation = false; //breakpoint here
                    break;
            }

            if (allow_propagation)
                base.WndProc(ref msg);
        }
    }
}

但断点永远不会触发。我做错了什么？覆盖WndProc这样的事情是常见的做法，但这里没有工作。

我试图阻止点击传播到文档，因此用户可以滚动它，但无法通过点击与其进行互动。