Introduce a kill-switch for shipping features.

BUILD.gn

 # Copyright 2014 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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
 v8_enable_handle_zapping = true
@@ skipping 178 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",
   ]
 
   outputs = [
     "$target_gen_dir/libraries.cc"
   ]
 
   if (v8_enable_i18n_support) {
     sources += [ "src/i18n.js" ]
   }
@@ skipping 18 matching lines @@
   script = "tools/js2c.py"
 
   # The script depends on this other script, this rule causes a rebuild if it
   # changes.
   source_prereqs = [ "tools/jsmin.py" ]
 
   sources = [
     "src/macros.py",
     "src/proxy.js",
     "src/generator.js",
+    "src/harmony-string.js",
     "src/harmony-array.js",
     "src/harmony-typedarray.js",
     "src/harmony-classes.js",
     "src/harmony-tostring.js",
     "src/harmony-templates.js"
   ]
 
   outputs = [
     "$target_gen_dir/experimental-libraries.cc"
   ]
@@ skipping 1196 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }