Provide iOS implementation of BookmarkServerClusterService factory
Expand the KeyedServiceProvider interface to allow creation of KeyedServices
required by BookmarkServerClusterService constructor and to give access to
the corresponding factories (for dependencies).
Implement iOS version of BookmarkServerClusterService factory and change the
iOS code to use that implementation instead of the one from //chrome.
BUG=429756
Review URL: https://codereview.chromium.org/
1159743005
Cr-Commit-Position: refs/heads/master@{#332375}