Enable 'about_page' API key on stable

chrome/common/extensions/api/_manifest_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 manifest keys 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:
 //
 // $ echo -n "aaaabbbbccccddddeeeeffffgggghhhh" | \
 // sha1sum | tr '[:lower:]' '[:upper:]'
 // 9A0417016F345C934A1A88F55CA17C05014EEEBA  -
 //
 // Google employees: please update http://go/chrome-api-whitelist to map
 // hashes back to ids.
 
 {
   "about_page": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["shared_module"]
   },
   "app": {
     "channel": "stable",
     "extension_types": ["legacy_packaged_app", "hosted_app", "platform_app"]
   },
   "app.isolation": {
     "channel": "stable",
     // Platform apps always have isolated storage, thus they cannot specify it
     // via the manifest.
@@ skipping 345 matching lines @@
   },
   "url_handlers": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
   "version": {
     "channel": "stable",
     "extension_types": "all"
   }
 }