Enabling webview in app_shell.

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 1039 matching lines @@
       "2779FA8B45841D61A37207CCFAC9CB393964FE5B"   // Login Proxy (prototype)
     ]
   },
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
-  },
-  "webview": [{
-    "channel": "stable",
-    "extension_types": ["platform_app"]
-  }, {
-    // General support for webview in component extensions still in progress.
-    // 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
-    ]
-  }]
+  }
 }