Enable the chrome.declarativeContent API on the stable channel.

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.
 
 // See c/c/e/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:
 //
 // $ echo -n "aaaabbbbccccddddeeeeffffgggghhhh" | \
@@ skipping 252 matching lines @@
         "FA0501B579070BB9CBD4FCAEC8CB0EDF22BA2F04", // Apps Editor published.
         "4A4EA121622FCA3D78ED2AB534197F43D7189EE0", // Spark nightly build
         "9FDE6E7F06FCFA11D9A05041C7FF6D8AE662F5D1"  // Spark release
     ]
   },
   "devtools": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "declarativeContent": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["extension"]
   },
   "declarativeWebRequest": [
     {
       "channel": "beta",
       "extension_types": ["extension", "legacy_packaged_app"]
     },
     {
       "channel": "stable",
       "extension_types": ["extension", "legacy_packaged_app"],
@@ skipping 654 matching lines @@
     // Only allowed for whitelisted extensions until all the caveats are
     // addressed. Tracked in crbug/285151.
     "channel": "stable",
     "extension_types": ["extension"],
     "location": "component",
     "whitelist": [
       "D519188F86D9ACCEE0412007B227D9936EB9676B"  // GAIA Component Extension
     ]
   }]
 }