<webview>: Implement support for package-local chrome-extension:// URLs

chrome/common/extensions/api/_manifest_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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "app": {
     "channel": "stable",
@@ skipping 366 matching lines @@
   },
   "version": {
     "channel": "stable",
     "extension_types": "all"
   },
   "web_accessible_resources": {
     "channel": "stable",
     "extension_types": [
       "extension", "legacy_packaged_app", "hosted_app"
     ]
+  },
+  "webview": {
+    "channel": "dev",
+    "extension_types": ["platform_app"],
+    "min_manifest_version": 2
   }
 }