Expose chrome.braveShields to brave-extension only

Fix brave/brave-browser#602

Author: bbondy

common/extensions/api/_api_features.json

@@ -1,12 +1,16 @@
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// Command to get whitelist ID: echo -n mnojpmjdmbbfmejpflffifhffcmidifd | openssl sha1
 
 {
   "braveShields": {
     "channel": "stable",
     "dependencies": [],
-    "contexts": ["blessed_extension"]
+    "contexts": ["blessed_extension"],
+    "whitelist": [
+      "A321D47A2B4CA86898167A55CA8B2E02385EA7CD"
+    ]
   },
   "topSites": [{
     "dependencies": ["permission:topSites"],