Don't try to set the cursor on null windows.

chrome/browser/renderer_host/render_widget_host_view_gtk.cc

 // Copyright (c) 2006-2008 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/renderer_host/render_widget_host_view_gtk.h"
 
 #include <gtk/gtk.h>
 #include <gdk/gdk.h>
 #include <cairo/cairo.h>
 
@@ skipping 322 matching lines @@
           damage_rect, x11_util::GetX11WindowFromGtkWidget(view_.get()));
     }
   } else {
     if (window)
       gdk_window_clear(window);
     NOTIMPLEMENTED();
   }
 }
 
 void RenderWidgetHostViewGtk::ShowCurrentCursor() {
+  // The widget may not have a window. If that's the case, abort mission. This
+  // is the same issue as that explained above in Paint().
+  if (!view_.get()->window)
+    return;
+
   GdkCursor* gdk_cursor;
   switch(current_cursor_.GetCursorType()) {
     case GDK_CURSOR_IS_PIXMAP:
       // TODO(port): WebKit bug https://bugs.webkit.org/show_bug.cgi?id=16388 is
       // that calling gdk_window_set_cursor repeatedly is expensive.  We should
       // avoid it here where possible.
       gdk_cursor = current_cursor_.GetCustomCursor();
       break;
 
     case GDK_LAST_CURSOR:
@@ skipping 15 matching lines @@
       break;
 
     default:
       gdk_cursor = gdk_cursor_new(current_cursor_.GetCursorType());
   }
   gdk_window_set_cursor(view_.get()->window, gdk_cursor);
   // The window now owns the cursor.
   if (gdk_cursor)
     gdk_cursor_unref(gdk_cursor);
 }