Start consolidating cross-port file selection code into ui/base/dialogs.

ui/base/dialogs/select_file_policy.h

+// Copyright (c) 2012 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.
+
+#ifndef UI_BASE_DIALOGS_SELECT_FILE_POLICY_H_
+#define UI_BASE_DIALOGS_SELECT_FILE_POLICY_H_
+#pragma once
+
+namespace ui {
+
+// An optional policy class that provides decisions on whether to allow showing
+// a native file dialog. Some ports need this.
+class SelectFilePolicy {
+ public:
+  virtual ~SelectFilePolicy() {}
+
+  // Returns true if the current policy allows for file selection dialogs.
+  virtual bool CanOpenSelectFileDialog() = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_DIALOGS_SELECT_FILE_POLICY_H_