Convert WindowOpenDisposition to an enum class.

ui/base/window_open_disposition.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/base/window_open_disposition.h"
 
 #include "build/build_config.h"
 #include "ui/events/event_constants.h"
 
 namespace ui {
 
 WindowOpenDisposition DispositionFromClick(bool middle_button,
                                            bool alt_key,
                                            bool ctrl_key,
                                            bool meta_key,
                                            bool shift_key) {
   // MacOS uses meta key (Command key) to spawn new tabs.
 #if defined(OS_MACOSX)
   if (middle_button || meta_key)
 #else
   if (middle_button || ctrl_key)
 #endif
-    return shift_key ? NEW_FOREGROUND_TAB : NEW_BACKGROUND_TAB;
+    return shift_key ? WindowOpenDisposition::NEW_FOREGROUND_TAB
+                     : WindowOpenDisposition::NEW_BACKGROUND_TAB;
   if (shift_key)
-    return NEW_WINDOW;
+    return WindowOpenDisposition::NEW_WINDOW;
   if (alt_key)
-    return SAVE_TO_DISK;
-  return CURRENT_TAB;
+    return WindowOpenDisposition::SAVE_TO_DISK;
+  return WindowOpenDisposition::CURRENT_TAB;
 }
 
 WindowOpenDisposition DispositionFromEventFlags(int event_flags) {
   return DispositionFromClick(
       (event_flags & ui::EF_MIDDLE_MOUSE_BUTTON) != 0,
       (event_flags & ui::EF_ALT_DOWN) != 0,
       (event_flags & ui::EF_CONTROL_DOWN) != 0,
       (event_flags & ui::EF_COMMAND_DOWN) != 0,
       (event_flags & ui::EF_SHIFT_DOWN) != 0);
 }
 
 }  // namespace ui