Make ContextualContentSuggestionsService a KeyedService that
is created by ContextualContentSuggestionsServiceFactory so it
can be used independently from ContentSuggestionsService.
The rename to ContextualContentSuggestionsService is
necessary because ContextualSuggestionsService is already
used in components/omnibox.

Bug: 749988
Change-Id: Ic4bdb7d7ec3937c8a46cf73c58c8caa2d94d3829
Reviewed-on: https://chromium-review.googlesource.com/613540


Commit-Queue: Andre Gaschler <gaschler@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494795}