XFCE disables the system decorations if there's an xshape set. So

chrome/browser/gtk/browser_window_gtk.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/gtk/browser_window_gtk.h"
 
 #include <gdk/gdkkeysyms.h>
 #include <X11/XF86keysym.h>
 
 #include "app/resource_bundle.h"
@@ skipping 1100 matching lines @@
     GdkRectangle mid_rect = { 1, 1, width - 2, 2 };
     GdkRectangle bot_rect = { 0, 3, width, height - 3 };
     GdkRegion* mask = gdk_region_rectangle(&top_rect);
     gdk_region_union_with_rect(mask, &mid_rect);
     gdk_region_union_with_rect(mask, &bot_rect);
     gdk_window_shape_combine_region(GTK_WIDGET(window_)->window, mask, 0, 0);
     gdk_region_destroy(mask);
     gtk_alignment_set_padding(GTK_ALIGNMENT(window_container_), 1,
         kFrameBorderThickness, kFrameBorderThickness, kFrameBorderThickness);
   } else {
-    // Disable rounded corners.  Simply passing in a NULL region doesn't
-    // seem to work on KWin, so manually set the shape to the whole window.
-    GdkRectangle rect = { 0, 0, width, height };
-    GdkRegion* mask = gdk_region_rectangle(&rect);
-    gdk_window_shape_combine_region(GTK_WIDGET(window_)->window, mask, 0, 0);
-    gdk_region_destroy(mask);
+    if (use_custom_frame_.GetValue()) {

[Evan Stade, 2009/07/08 23:02:39]

can you put the first line of the desc. as a comment here?

+      // Disable rounded corners.  Simply passing in a NULL region doesn't
+      // seem to work on KWin, so manually set the shape to the whole window.
+      GdkRectangle rect = { 0, 0, width, height };
+      GdkRegion* mask = gdk_region_rectangle(&rect);
+      gdk_window_shape_combine_region(GTK_WIDGET(window_)->window, mask, 0, 0);
+      gdk_region_destroy(mask);
+    } else {
+      gdk_window_shape_combine_region(GTK_WIDGET(window_)->window, NULL, 0, 0);
+    }
     gtk_alignment_set_padding(GTK_ALIGNMENT(window_container_), 0, 0, 0, 0);
   }
 }
 
 void BrowserWindowGtk::ConnectAccelerators() {
   GtkAccelGroup* accel_group = gtk_accel_group_new();
   gtk_window_add_accel_group(window_, accel_group);
   // Drop the initial ref on |accel_group| so |window_| will own it.
   g_object_unref(accel_group);
 
@@ skipping 254 matching lines @@
       *edge = GDK_WINDOW_EDGE_NORTH_EAST;
     } else if (y < bounds_.height() - kResizeAreaCornerSize) {
       *edge = GDK_WINDOW_EDGE_EAST;
     } else {
       *edge = GDK_WINDOW_EDGE_SOUTH_EAST;
     }
     return true;
   }
   NOTREACHED();
 }