Implement kiosk multiple apps feature.

extensions/common/api/_manifest_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 manifest keys implemented under src/extensions.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
 //
@@ skipping 157 matching lines @@
     "extension_types": [
       "platform_app"
     ]
   },
   "kiosk_only": {
     "channel": "dev",
     "extension_types": [
       "platform_app"
     ]
   },
+  "kiosk_secondary_apps": {
+    "channel": "stable",
+    "extension_types": [
+      "platform_app"
+    ]   
+  },
   "launcher_page": {
     "channel": "stable",
     "min_manifest_version": 2,
     "extension_types": ["platform_app"],
     "whitelist": [
       "07BD6A765FFC289FF755D7CAB2893A40EC337FEC",  // http://crbug.com/404000
       "896B85CC7E913E11C34892C1425A093C0701D386",  // http://crbug.com/404000
       "11A01C82EF355E674E4F9728A801F5C3CB40D83F",  // http://crbug.com/404000
       "F410C88469990EE7947450311D24B8AF2ADB2595"   // http://crbug.com/404000
     ]
@@ skipping 109 matching lines @@
       "extension_types": ["platform_app"],
       "location": "component"
     }
   ],
   "webview": {
     "channel": "stable",
     "extension_types": ["platform_app"],
     "min_manifest_version": 2
   }
 }