Sort out build dependencies for LinuxUI.

ui/shell_dialogs/linux_shell_dialog.cc

+// Copyright (c) 2013 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 "ui/shell_dialogs/linux_shell_dialog.h"
+
+namespace {
+
+ui::LinuxShellDialog* g_linux_shell_dialog = NULL;
+
+}  // namespace
+
+namespace ui {
+
+void LinuxShellDialog::SetInstance(LinuxShellDialog* instance) {
+  g_linux_shell_dialog = instance;
+}
+
+const LinuxShellDialog* LinuxShellDialog::instance() {
+  return g_linux_shell_dialog;
+}
+
+}  // namespace ui