WIP: diff which plumbs through the event URL.

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 96 matching lines @@
     "contexts": ["blessed_extension"]
   },
   "sockets.udp": {
     "dependencies": ["manifest:sockets"],
     "contexts": ["blessed_extension"]
   },
   "storage": {
     "dependencies": ["permission:storage"],
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
-  "test": {
+  "test": [{
     "internal": true,
     "channel": "stable",
     "extension_types": "all",
-    // Everything except web pages.
-    "contexts": [
-      "blessed_extension",
-      "content_script",
-      "unblessed_extension",
-      "webui"
+    // Everything except web pages and WebUI. WebUI is declared in a separate
+    // rule to keep the "matches" property isolated.
+    "contexts": ["blessed_extension", "content_script", "unblessed_extension"]
+  }, {
+    "internal": true,
+    "channel": "stable",
+    "contexts": ["webui"],
+    "matches": [
+      "chrome://extensions-frame/*"
     ]
-  },
+  }],
   "types": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "contexts": ["blessed_extension"]
   },
   "types.private": {
     "channel": "dev",
     "extension_types": ["extension"],
     "location": "component"
   },
   "usb": {
     "dependencies": ["permission:usb"],
     "contexts": ["blessed_extension"]
   }
 }