Add support for app_shell-only extension APIs

extensions/shell/common/api/_api_features.json

Index: extensions/shell/common/api/_api_features.json
diff --git a/extensions/shell/common/api/_api_features.json b/extensions/shell/common/api/_api_features.json
new file mode 100644
index 0000000000000000000000000000000000000000..b4a137618a158b9d4438aa08ed984b08cbac6ed0
--- /dev/null
+++ b/extensions/shell/common/api/_api_features.json
@@ -0,0 +1,15 @@
+// Copyright 2014 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 file defines extension APIs implemented under src/extensions/shell.
+// See extensions/common/features/* to understand this file, in particular
+// feature.h, simple_feature.h, and base_feature_provider.h.
+
+{
+  "shell.identity": {
+    "channel": "dev",
+    "contexts": ["blessed_extension"],
+    "extension_types": ["platform_app"]
+  }
+}