Support webview tag in component extension

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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "activeTab": {
     "channel": "stable",
@@ skipping 748 matching lines @@
     ]
   },
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   },
-  "webview": {
+  "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": [
+      "mfffpogegjflfpflabcdkioaeobkgjik"  // GAIA Component Extension
+    ]
+  }]
 }