DevTools: introduce screencast experiment.

Source/devtools/devtools.gyp

 #
 # 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 121 matching lines @@
             'front_end/PropertiesSection.js',
             'front_end/RemoteObject.js',
             'front_end/Resource.js',
             'front_end/ResourceScriptMapping.js',
             'front_end/ResourceTreeModel.js',
             'front_end/ResourceType.js',
             'front_end/ResourceUtils.js',
             'front_end/ResourceView.js',
             'front_end/RuntimeModel.js',
             'front_end/SASSSourceMapping.js',
+            'front_end/ScreencastView.js',
             'front_end/Script.js',
             'front_end/ScriptFormatter.js',
             'front_end/ScriptFormatterWorker.js',
             'front_end/ScriptSnippetModel.js',
             'front_end/ScriptsPanelDescriptor.js',
             'front_end/SearchController.js',
             'front_end/SettingsScreen.js',
             'front_end/Section.js',
             'front_end/Settings.js',
             'front_end/ShortcutsScreen.js',
@@ skipping 757 matching lines @@
                         'destination': '<(PRODUCT_DIR)/resources/inspector',
                         'files': [
                             '<@(devtools_standalone_files)',
                         ],
                     }],
                 },
             ],
         }],
     ], # conditions
 }