Enable webview tag in webui

extensions/common/api/_api_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 extension APIs implemented under src/extensions.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 55 matching lines @@
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "contexts": ["blessed_extension"]
   },
   "guestViewInternal": [
     {
       "internal": true,
       "channel": "stable",
       "contexts": ["blessed_extension"]
     }, {
-      // Component extensions can use the guestViewInternal API from iframes.
-      "location": "component",
-      "internal": true,
-      "dependencies": ["permission:webview"],
-      "contexts": ["unblessed_extension"]
-    }, {
       "internal": true,
       "channel": "trunk",
       "contexts": ["webui"],
-      "matches": ["chrome://extensions-frame/*", "chrome://extensions/*"]
+      "matches": [
+        "chrome://extensions-frame/*",
+        "chrome://extensions/*",
+        "chrome://chrome-signin/*"
+      ]
     }
   ],
   "hid": {
     "dependencies": ["permission:hid"],
     "contexts": ["blessed_extension"]
   },
   "power": {
     "dependencies": ["permission:power"],
     "contexts": ["blessed_extension"]
   },
@@ skipping 149 matching lines @@
       "E703483CEF33DEC18B4B6DD84B5C776FB9182BDB",
       "1A26E32DE447A17CBE5E9750CDBA78F58539B39C",
       "59048028102D7B4C681DBC7BC6CD980C3DC66DA3"
     ]
   }],
   "webViewInternal": [{
     "internal": true,
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   }, {
-    // Component extensions can use the webViewInternal API from iframes.
-    "location": "component",
     "internal": true,
-    "dependencies": ["permission:webview"],
-    "contexts": ["unblessed_extension"]
+    "channel": "dev",
+    "contexts": ["webui"],
+    "matches": ["chrome://chrome-signin/*"]
   }]
 }