Added wxWindow::IsDescendant() helper.

This function checks if another window is a direct or indirect child of this
one, which can be needed in a number of situations.

See #3063.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71024 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -1242,9 +1242,28 @@ void wxWindowBase::Thaw()
 }
 
 // ----------------------------------------------------------------------------
-// reparenting the window
+// Dealing with parents and children.
 // ----------------------------------------------------------------------------
 
+bool wxWindowBase::IsDescendant(wxWindowBase* win) const
+{
+    // Iterate until we find this window in the parent chain or exhaust it.
+    while ( win )
+    {
+        wxWindow* const parent = win->GetParent();
+        if ( parent == this )
+            return true;
+
+        // Stop iterating on reaching the top level window boundary.
+        if ( parent->IsTopLevel() )
+            break;
+
+        win = parent;
+    }
+
+    return false;
+}
+
 void wxWindowBase::AddChild(wxWindowBase *child)
 {
     wxCHECK_RET( child, wxT("can't add a NULL child") );