Introduce a kill-switch for shipping features.

tools/gyp/v8.gyp

 # Copyright 2012 the V8 project authors. 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
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1606 matching lines @@
           '../../src/weak-collection.js',
           '../../src/collection-iterator.js',
           '../../src/promise.js',
           '../../src/messages.js',
           '../../src/json.js',
           '../../src/array-iterator.js',
           '../../src/string-iterator.js',
           '../../src/debug-debugger.js',
           '../../src/mirror-debugger.js',
           '../../src/liveedit-debugger.js',
-          '../../src/harmony-string.js',
           '../../src/macros.py',
         ],
         'experimental_library_files': [
           '../../src/macros.py',
           '../../src/proxy.js',
           '../../src/generator.js',
+          '../../src/harmony-string.js',
           '../../src/harmony-array.js',
           '../../src/harmony-tostring.js',
           '../../src/harmony-typedarray.js',
           '../../src/harmony-classes.js',
           '../../src/harmony-templates.js'
         ],
         'libraries_bin_file': '<(SHARED_INTERMEDIATE_DIR)/libraries.bin',
         'libraries_experimental_bin_file': '<(SHARED_INTERMEDIATE_DIR)/libraries-experimental.bin',
       },
       'actions': [
@@ skipping 98 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }