Introduce BookmarkClient interface to abstract embedder

chrome/browser/history/DEPS

 include_rules = [
   # History is being made into a Browser Component, so we have these
   # basic rules followed by temporary exceptions.  Please don't
   # add to the list of exceptions!
   "-chrome/browser",
   "+chrome/browser/chrome_notification_types.h",
   "+chrome/browser/common",
   "+chrome/browser/favicon",
   "+chrome/browser/history",
   "+chrome/browser/network_time",
   "+chrome/tools/profiles",  # For history unit tests.
   "+components/visitedlink/browser",
 
   # TODO(erikwright): Bring this list to zero.
   #
   # Do not add to the list of temporarily-allowed dependencies below,
   # and please do not introduce more #includes of these files.
   "!chrome/browser/autocomplete/autocomplete_match.h",
   "!chrome/browser/autocomplete/autocomplete_provider.h",
   "!chrome/browser/autocomplete/autocomplete_result.h",
   "!chrome/browser/autocomplete/history_provider_util.h",
   "!chrome/browser/autocomplete/history_url_provider.h",
   "!chrome/browser/autocomplete/url_prefix.h",
   "!chrome/browser/bookmarks/bookmark_model.h",
   "!chrome/browser/bookmarks/bookmark_model_factory.h",
   "!chrome/browser/bookmarks/bookmark_utils.h",
+  "!chrome/browser/bookmarks/test_bookmark_client.h",
   "!chrome/browser/browser_process.h",
   "!chrome/browser/chromeos/login/existing_user_controller.h",
   "!chrome/browser/content_settings/cookie_settings.h",
   "!chrome/browser/diagnostics/sqlite_diagnostics.h",
   "!chrome/browser/omnibox/omnibox_field_trial.h",
   "!chrome/browser/omnibox/omnibox_log.h",
   "!chrome/browser/prefs/scoped_user_pref_update.h",
   "!chrome/browser/prerender/prerender_contents.h",
   "!chrome/browser/prerender/prerender_manager.h",
   "!chrome/browser/prerender/prerender_manager_factory.h",
@@ skipping 24 matching lines @@
   ],
   # TODO(erikwright): Bring this list to zero.
   #
   # Do not add to the list of temporarily-allowed dependencies below,
   # and please do not introduce more #includes of these files.
   '.*_[a-z]*test\.cc': [
     "!chrome/browser/bookmarks/bookmark_test_helpers.h",
     "!chrome/browser/bookmarks/bookmark_utils.h",
   ]
 }