Chiudere popup?

[siteper]

Ragazzi qualcuno sa come si fa a chiudere una finestra popup?
cioè in una form1 con un webbrowser che naviga su(" es www.google.it")
quando cerco di chiudere la pagina si apre una popup chiedendomi esci dalla pagina? oppure rimani..(oppure mi dice vuoi veramente abbandonare la pagina,cioè qualcosa di simile.
Vorrei cliccare su esci dalla pagina però non so proprio da dove cominciare.Ho visto su internet ma molte guide non funzionano.
Qualcuno sa come si fa?
Magari indicarmi qualche guida o qualcosa da leggere a riguardo.
Chiedo scusa se esiste già una discussione simile ma ho cercato prima ma non ho trovato niente.
Grazie in anticipo

[siteper]

questo è il codice che ho trovato in rete:

Imports System.Runtime.InteropServices

Public Class DialogHandler
    'API CONSTANTS
    Const WM_GETTEXT As Long = &HD
    Const WM_GETTEXTLENGTH As Long = &HE
    Const GW_ENABLEDPOPUP As Long = 6
    Const BM_CLICK As Long = &HF5&
    Const GW_CHILD As Long = 5
    Const GW_HWNDNEXT As Long = 2

    'FINDS CHILD WINDOWS
    Private Declare Auto Function GetWindow Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal uCmd As Integer) As IntPtr

    'SEND MESSAGES TO THE BUTTON
    Private Declare Auto Function SendMessage Lib "user32.dll" Alias "SendMessage" (ByVal hWnd As IntPtr, ByVal Msg As Integer, _
    ByVal wParam As Integer, ByRef lParam As IntPtr) As IntPtr

    'GETS WINDOW TEXT
    Private Declare Auto Function SendMessageA Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal Msg As Integer, _
    ByVal wParam As IntPtr, ByRef lParam As IntPtr) As IntPtr
    <DllImport("User32.dll", CharSet:=CharSet.Auto, Entrypoint:="SendMessage")> Public Shared Function SendMessageString(ByVal hwnd As IntPtr, _
    ByVal wMsg As Integer, ByVal wparam As Integer, ByVal lparam As System.Text.StringBuilder) As IntPtr
    End Function

    Private Function GetChildWindowHandles(ByVal ParentWindowHandle As IntPtr) As ArrayList

        Dim ptrChild As IntPtr
        Dim clsRet As New ArrayList

        'GET FIRST CHILD HANDLE
        ptrChild = GetChildWindowHandle(ParentWindowHandle)

        Do Until ptrChild.Equals(IntPtr.Zero)
            'ADD TO COLLECTION OF HANDLES
            clsRet.Add(ptrChild)
            'GET NEXT CHILD
            ptrChild = GetNextWindowHandle(ptrChild)
        Loop

        Return clsRet

    End Function

    Private Function GetChildWindowHandle(ByVal ParentWindowHandle As IntPtr) As IntPtr
        Return GetWindow(ParentWindowHandle, GW_CHILD)
    End Function

    Private Function GetNextWindowHandle(ByVal CurrentWindowhandle As IntPtr) As IntPtr
        Return GetWindow(CurrentWindowhandle, GW_HWNDNEXT)
    End Function

    'RETURNS TEXT OF THE WINDOW FOR CONFIRMATION OF CORRECT DIALOG
    Private Function GetWindowText(ByVal WindowHandle As IntPtr) As String

        Dim ptrRet As IntPtr
        Dim ptrLength As IntPtr

        'LENGTH OF BUFFER
        ptrLength = SendMessageA(WindowHandle, WM_GETTEXTLENGTH, IntPtr.Zero, IntPtr.Zero)

        'BUFFER NEEDED FOR RETURN VALUE
        Dim sb As New System.Text.StringBuilder(ptrLength.ToInt32 + 1)

        'WINDOW TEXT
        ptrRet = SendMessageString(WindowHandle, WM_GETTEXT, ptrLength.ToInt32 + 1, sb)

        Return sb.ToString

    End Function

    'SEND A 'CLICK' TO THE BUTTON ("WINDOW")
    Private Sub PerformClick(ByVal WindowHandle As IntPtr)
        SendMessage(WindowHandle, BM_CLICK, 0, IntPtr.Zero)
    End Sub

    Public Sub LookForAndCloseIEPopup(ByVal whichButton As String)

        'GET HANDLE OF ANY POPUP WINDOW ASSOCIATED WITH MAIN FORM
        Dim ptrDialogWindow As IntPtr = GetWindow(Process.GetCurrentProcess.MainWindowHandle, GW_ENABLEDPOPUP)

        'IF IT'S A BROWSER POPUP, HANDLE IT
        If GetWindowText(ptrDialogWindow) = "Microsoft Internet Explorer" Or GetWindowText(ptrDialogWindow) = "Message from webpage" Or GetWindowText(ptrDialogWindow) = "Windows Internet Explorer" Then
            ClosePopup(ptrDialogWindow, whichButton)
        End If

    End Sub

    Private Sub ClosePopup(ByVal WindowHandle As IntPtr, ByVal whichButton As String)

        Dim clsChildHandles As ArrayList = GetChildWindowHandles(WindowHandle)

        For Each ptrHandle As IntPtr In clsChildHandles
            'IF IT FINDS A BUTTON WITH THE TEXT SPECIFIED, CLICK IT
            If GetWindowText(ptrHandle).Contains(whichButton) Then PerformClick(ptrHandle) : Exit For
        Next

    End Sub
End Class

Solo che Io sto utilizzando visualbasic 2010 e mi da errore nelle seguenti righe:

api constants
= &HD
= &HE
= &HF5&

come li devo scrivere per non darmi l'errore?
Si capisce che sono un principiante quindi vi chiedo scusa per il disturbo e grazie per la pazienza.