Componentize OriginsSeenService & provide iOS factory.

components/navigation_metrics.gypi

 # Copyright 2013 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.
 
 {
   'targets': [
     {
       'target_name': 'navigation_metrics',
       'type': 'static_library',
       'dependencies': [
         '../base/base.gyp:base',
         '../url/url.gyp:url_lib',
+        'keyed_service_core',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
         'navigation_metrics/navigation_metrics.cc',
         'navigation_metrics/navigation_metrics.h',
+        'navigation_metrics/origins_seen_service.cc',
+        'navigation_metrics/origins_seen_service.h',
       ],
     },
   ],
 }