Add GDK_DEBUG=frames

Add a debug option to print out detailed statistics about each frame drawn.

https://bugzilla.gnome.org/show_bug.cgi?id=685460

gdk/x11/gdkdisplay-x11.c

@@ -1155,6 +1155,11 @@ _gdk_wm_protocols_filter (GdkXEvent *xev,
                 gdk_frame_timings_set_refresh_interval (timings, refresh_interval);
 
               gdk_frame_timings_set_complete (timings, TRUE);
+#ifdef G_ENABLE_DEBUG
+              if ((_gdk_debug_flags & GDK_DEBUG_FRAMES) != 0)
+                _gdk_frame_history_debug_print (gdk_frame_clock_get_history (clock),
+                                                timings);
+#endif /* G_ENABLE_DEBUG */
             }
         }
     }

gdk/x11/gdkwindow-x11.c

@@ -322,6 +322,18 @@ gdk_x11_window_end_frame (GdkWindow *window)
 
   if (impl->toplevel->current_counter_value % 2 == 1)
     {
+#ifdef G_ENABLE_DEBUG
+      if ((_gdk_debug_flags & GDK_DEBUG_FRAMES) != 0)
+        {
+          XImage *image = XGetImage (GDK_WINDOW_XDISPLAY (window),
+                                     GDK_WINDOW_XID (window),
+                                     0, 0, 1, 1,
+                                     (1 << 24) - 1,
+                                     ZPixmap);
+          XDestroyImage (image);
+        }
+#endif /* G_ENABLE_DEBUG */
+
       /* An increment of 3 means that the frame was not drawn as fast as possible,
        * but rather at a particular time. This can trigger different handling from
        * the compositor.