DevTools: Remove unused frontend code

Source/devtools/devtools.gypi

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #         * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #         * Redistributions in binary form must reproduce the above
@@ skipping 204 matching lines @@
         ],
         'devtools_ui_js_files': [
             'front_end/ui/dataGrid.css',
             'front_end/ui/filter.css',
             'front_end/ui/flameChart.css',
             'front_end/ui/helpScreen.css',
             'front_end/ui/overviewGrid.css',
             'front_end/ui/panelEnablerView.css',
             'front_end/ui/pieChart.css',
             'front_end/ui/ActionRegistry.js',
-            'front_end/ui/Checkbox.js',
             'front_end/ui/CompletionDictionary.js',
             'front_end/ui/Context.js',
             'front_end/ui/ContextMenu.js',
             'front_end/ui/DataGrid.js',
             'front_end/ui/Dialog.js',
             'front_end/ui/DOMSyntaxHighlighter.js',
             'front_end/ui/DropDownMenu.js',
             'front_end/ui/EmptyView.js',
             'front_end/ui/FilterBar.js',
             'front_end/ui/FlameChart.js',
@@ skipping 434 matching lines @@
             'front_end/Images/touchCursor.png',
             'front_end/Images/touchCursor_2x.png',
             'front_end/Images/transformControls.png',
             'front_end/Images/transformControls_2x.png',
         ],
         'devtools_extension_api_files': [
             'front_end/extensions/ExtensionAPI.js',
         ],
     },
 }