Split Toplevel::getWmClientLeader in two parts

First part (fetch) just creates the Xcb::Property while the
second part (read) reads the property. This allows to better
schedule the commands in Client::manage to reduce the number of
roundtrips. This reduces the time spent for fetching the client
leader property by about half a millisecond on my system.

manage.cpp

@@ -97,6 +97,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
         NET::WM2Protocols |
         NET::WM2InitialMappingState;
 
+    auto wmClientLeaderCookie = fetchWmClientLeader();
     info = new WinInfo(this, m_client, rootWindow(), properties, properties2);
 
     // If it's already mapped, ignore hint
@@ -105,7 +106,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
     m_colormap = attr->colormap;
 
     getResourceClass();
-    getWmClientLeader();
+    readWmClientLeader(wmClientLeaderCookie);
     getWmClientMachine();
     getSyncCounter();
     // First only read the caption text, so that setupWindowRules() can use it for matching,

toplevel.cpp

@@ -145,10 +145,20 @@ QRect Toplevel::visibleRect() const
     return r.translated(geometry().topLeft());
 }
 
+Xcb::Property Toplevel::fetchWmClientLeader() const
+{
+    return Xcb::Property(false, window(), atoms->wm_client_leader, XCB_ATOM_WINDOW, 0, 10000);
+}
+
+void Toplevel::readWmClientLeader(Xcb::Property &prop)
+{
+    wmClientLeaderWin = prop.value<xcb_window_t>(window());
+}
+
 void Toplevel::getWmClientLeader()
 {
-    Xcb::Property prop(false, window(), atoms->wm_client_leader, XCB_ATOM_WINDOW, 0, 10000);
-    wmClientLeaderWin = prop.value<xcb_window_t>(window());
+    auto prop = fetchWmClientLeader();
+    readWmClientLeader(prop);
 }
 
 /*!

toplevel.h

@@ -414,6 +414,8 @@ protected:
     virtual void damageNotifyEvent();
     void discardWindowPixmap();
     void addDamageFull();
+    Xcb::Property fetchWmClientLeader() const;
+    void readWmClientLeader(Xcb::Property &p);
     void getWmClientLeader();
     void getWmClientMachine();
     /**