Register a Service Worker when an extension is enabled.

chrome/browser/extensions/DEPS

 include_rules = [
   # TODO(benwells): Once the extensions component is established
   # and there are only chrome specific extension things left in
   # chrome/browser/extensions, the restriction of not being able
   # to depend on apps will be lifted.
   "-apps",
   "+apps/app_window.h",
   "+apps/app_window_registry.h",
   "-chrome/browser/apps",
 
   # TODO(tfarina): Remove all these. crbug.com/125846.
   # DO NOT ADD ANY MORE ITEMS TO THE LIST BELOW!
   "!chrome/browser/ui/views/extensions/extension_view_views.h",
   # DO NOT ADD ANY MORE ITEMS TO THE ABOVE LIST!
 
   # For access to testing command line switches.
   "+ppapi/shared_impl",
+
+  "+content",
 ]
 
 specific_include_rules = {
   # The extensions client interface is the master arbiter of which
   # API functions exist, so it needs to know about app APIs.
   "chrome_extensions_browser_client\.cc": [
      "+apps/common/api/generated_api.h",
   ],
 }