RenderWidget popup should be a NSWindow so it can go outside the main window.

ui/ui.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     'ui_resources.gypi',
@@ skipping 72 matching lines @@
         'base/clipboard/clipboard_util_win.h',
         'base/clipboard/clipboard_win.cc',
         'base/clipboard/custom_data_helper.cc',
         'base/clipboard/custom_data_helper.h',
         'base/clipboard/custom_data_helper_mac.mm',
         'base/clipboard/custom_data_helper_x.cc',
         'base/clipboard/scoped_clipboard_writer.cc',
         'base/clipboard/scoped_clipboard_writer.h',
         'base/cocoa/base_view.h',
         'base/cocoa/base_view.mm',
+        'base/cocoa/event_hook_application.h',
+        'base/cocoa/event_hook_application.mm',
         'base/cocoa/events_mac.mm',
         'base/cocoa/find_pasteboard.h',
         'base/cocoa/find_pasteboard.mm',
         'base/cocoa/focus_tracker.h',
         'base/cocoa/focus_tracker.mm',
         'base/cocoa/fullscreen_window_manager.h',
         'base/cocoa/fullscreen_window_manager.mm',
         'base/cocoa/nib_loading.h',
         'base/cocoa/nib_loading.mm',
         'base/cocoa/underlay_opengl_hosting_window.h',
@@ skipping 787 matching lines @@
            },
            'dependencies': [
              '../base/base.gyp:base_java',
            ],
            'includes': [ '../build/java.gypi' ],
          },
        ],
     }],
   ],
 }