app_shell: Add experimental shellPrivate extension API

extensions/common/api/_api_features.json

 // 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 features file defines extension APIs implemented under src/extensions.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 152 matching lines @@
     ],
     "matches": ["<all_urls>"]
   },
   "runtime.setUninstallURL": {
     "channel": "dev"
   },
   "serial": {
     "dependencies": ["permission:serial"],
     "contexts": ["blessed_extension"]
   },
+  "shellPrivate": {
+    "channel": "trunk",
+    "extension_types": ["platform_app"],
+    "contexts": ["blessed_extension"]
+  },
   "socket": {
     "dependencies": ["permission:socket"],
     "contexts": ["blessed_extension"]
   },
   "sockets.tcp": {
     "dependencies": ["manifest:sockets"],
     "contexts": ["blessed_extension"]
   },
   "sockets.tcpServer": {
     "dependencies": ["manifest:sockets"],
@@ skipping 110 matching lines @@
   }],
   "webViewRequest": [{
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": ["chrome://chrome-signin/*"]
   }]
 }