app_shell: Initial skeleton of a GCD target device setup API

extensions/shell/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 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.
 
 {
   // Stub implementation of chrome.identity for app_shell.
   "identity": {
     "channel": "dev",
     "contexts": ["blessed_extension"],
     "extension_types": ["platform_app"]
   },
+  // Setup related functions for a Google Cloud Devices (GCD) target device.
+  "shell.gcd": {
+    "channel": "dev",
+    "contexts": ["blessed_extension"],
+    "extension_types": ["platform_app"]    
+  },
   "shell.window": {
     "channel": "dev",
     "contexts": ["blessed_extension"],
     "extension_types": ["platform_app"]
   }
 }