Implement externally_connectable! Web pages can now communicate directly with

chrome/common/extensions/api/_permission_features.json

Index: chrome/common/extensions/api/_permission_features.json
diff --git a/chrome/common/extensions/api/_permission_features.json b/chrome/common/extensions/api/_permission_features.json
index 06e90a81c2f06556fd599d73b525d2c818c1a7af..73f925c471a4d0701492c06f12ea2ba12fe274cf 100644
--- a/chrome/common/extensions/api/_permission_features.json
+++ b/chrome/common/extensions/api/_permission_features.json
@@ -2,6 +2,9 @@
 // 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.
+
 {
   "activeTab": {
     "channel": "stable",