Implement <appview> skeleton.

chrome/common/extensions/api/_permission_features.json

 // Copyright (c) 2012 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 permissions for extension APIs implemented
 // under src/chrome.
 // 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 33 matching lines @@
     "channel": "stable",
     "extension_types": ["extension", "platform_app"],
     "whitelist": [
       "EE17C698905F7F2E6DDC87C9C30F11E164C829F4",  // Watchdog release
       "90113DA9516526D24DAF156C629CC41C049E8882",  // Watchdog testing
       "A9EFD71948A480C87D3B7C758FD938215F445F00",   // Obsolete
       "AE27D69DBE571F4B1694F05C89B710C646792231", // Published ADT.
       "5107DE9024C329EEA9C9A72D94C16723790C6422"  // Apps Developer Tool Dev.
     ]
   },
+  "appview": {
+    "channel": "dev",
+    "extension_types": ["platform_app"]
+  },
   "alarms": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "min_manifest_version": 2
   },
   "app.window.alwaysOnTop": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
   "app.window.fullscreen": {
@@ skipping 1018 matching lines @@
     // Only allowed for whitelisted extensions until all the caveats are
     // addressed. Tracked in crbug/285151.
     "channel": "stable",
     "extension_types": ["extension"],
     "location": "component",
     "whitelist": [
       "D519188F86D9ACCEE0412007B227D9936EB9676B"  // GAIA Component Extension
     ]
   }]
 }