Add support for command line switches to Features, and as proof that it works,

chrome/common/extensions/api/_permission_features.json

 // 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.
 
 // This features file defines permissions for extension APIs implemented
 // under src/chrome.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
@@ skipping 361 matching lines @@
   },
   "experienceSamplingPrivate": {
     "channel": "stable",
     "extension_types": ["extension"],
     "whitelist": [
       "0B5B953E53AC1859AC1DD3F67E115D1A5C2D6123"  // https://crbug.com/384635
     ]
   },
   "experimental": {
     "channel": "stable",
+    "command_line_switch": "experimental-extension-apis",
     "extension_types": [
       "extension", "legacy_packaged_app", "hosted_app", "platform_app"
     ]
   },
   "feedbackPrivate": {
     "channel": "stable",
     "extension_types": ["extension", "platform_app"],
     "whitelist": [
       "7910EAFDAF64B947E1CB31B333A9BD14CA556B6C",  // Feedback UI.
       "1C93BD3CF875F4A73C0B2A163BB8FBDA8B8B3D80",  // http://crbug.com/293683
@@ skipping 658 matching lines @@
   "webstorePrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "hosted_app"],
     "whitelist": [
       "B44D08FD98F1523ED5837D78D0A606EA9D6206E5",  // Web Store
       "2653F6F6C39BC6EEBD36A09AFB92A19782FF7EB4",  // Enterprise Web Store
       "2779FA8B45841D61A37207CCFAC9CB393964FE5B"   // Login Proxy (prototype)
     ]
   }
 }