Declare providing extension capabilities in the manifest.

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:
 //
@@ skipping 134 matching lines @@
     {
       "channel": "stable",
       "extension_types": ["extension", "legacy_packaged_app"]
     },
     {
       "channel": "stable",
       "extension_types": ["platform_app"],
       "location": "component"
     }
   ],
+  "file_system_provider": [
+    {
+      "channel": "dev",
+      "extension_types": ["extension", "platform_app"]
+    }
+  ],
   "homepage_url": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "import": {
     "channel": "stable",
     "extension_types": "all"
   },
   "input_components": {
     "channel": "stable",
@@ skipping 91 matching lines @@
   },
   "update_url": {
     "channel": "stable",
     "extension_types": "all"
   },
   "url_handlers": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   }
 }