xcb: Set WM_CLIENT_MACHINE property

It can be useful to detect that a window belongs to an
application running on a remote host. E.g. a window manager
may display the name of the remote host in the window title.
Or it can detect whether a client can be killed.

This property is set by Xlib's function XSetWMProperties(),
which is called by GTK and Qt 4, so it's also good to do
for consistency.

Change-Id: I0693156635cb2696b2fbe7006cbecb25d2680513
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -1821,6 +1821,7 @@ static const char * xcb_atomnames = {
     "WM_CLIENT_LEADER\0"
     "WM_WINDOW_ROLE\0"
     "SM_CLIENT_ID\0"
+    "WM_CLIENT_MACHINE\0"
 
     // Clipboard
     "CLIPBOARD\0"

src/plugins/platforms/xcb/qxcbconnection.h

@@ -119,6 +119,7 @@ namespace QXcbAtom {
         WM_CLIENT_LEADER,
         WM_WINDOW_ROLE,
         SM_CLIENT_ID,
+        WM_CLIENT_MACHINE,
 
         // Clipboard
         CLIPBOARD,

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -490,6 +490,13 @@ void QXcbWindow::create()
                         atom(QXcbAtom::_NET_WM_PID), XCB_ATOM_CARDINAL, 32,
                         1, &pid);
 
+    const QByteArray clientMachine = QSysInfo::machineHostName().toLocal8Bit();
+    if (!clientMachine.isEmpty()) {
+        xcb_change_property(xcb_connection(), XCB_PROP_MODE_REPLACE, m_window,
+                            atom(QXcbAtom::WM_CLIENT_MACHINE), XCB_ATOM_STRING, 8,
+                            clientMachine.size(), clientMachine.constData());
+    }
+
     xcb_wm_hints_t hints;
     memset(&hints, 0, sizeof(hints));
     xcb_wm_hints_set_normal(&hints);