browser: Abstract message box dialog functions into its own header file.

chrome/browser/simple_message_box.h

+// Copyright (c) 2011 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 CHROME_BROWSER_SIMPLE_MESSAGE_BOX_H_
+#define CHROME_BROWSER_SIMPLE_MESSAGE_BOX_H_
+#pragma once
+
+#include "base/string16.h"
+#include "ui/gfx/native_widget_types.h"
+
+namespace browser {
+
+// Pops up an error box with an OK button. If |parent| is non-null, the box
+// will be modal on it. (On Mac, it is always app-modal.) Generally speaking,
+// this function should not be used for much. Infobars are preferred.
+void ShowErrorBox(gfx::NativeWindow parent,
+                  const string16& title,
+                  const string16& message);
+
+// Pops up a dialog box with two buttons (Yes/No), with the default button of
+// Yes. If |parent| is non-null, the box will be modal on it. (On Mac, it is
+// always app-modal.) Returns true if the Yes button was chosen.
+bool ShowYesNoBox(gfx::NativeWindow parent,
+                  const string16& title,
+                  const string16& message);
+
+}  // namespace browser
+
+#endif  // CHROME_BROWSER_SIMPLE_MESSAGE_BOX_H_