Add ref count to service workers for extension API.

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 chrome/common/extensions/api/_features.md to understand this file, as
 // well as 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 428 matching lines @@
   },
   "test": [{
     "channel": "stable",
     "extension_types": "all",
     // Everything except web pages and WebUI. WebUI is declared in a separate
     // rule to keep the "matches" property isolated.
     "contexts": [
       "blessed_extension",
       "blessed_web_page",
       "content_script",
+      "extension_service_worker",
       "unblessed_extension"
     ]
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": [
       "chrome://extensions/*",
       "chrome://extensions-frame/*",
       "chrome://chrome/extensions/*"
     ]
@@ skipping 58 matching lines @@
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": [
       "chrome://chrome-signin/*",
       "chrome://media-router/*",
       "chrome://oobe/*"
     ]
   }]
 }