The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6dd692b945fc8599a4c7db22854d19c9b27d0d4c

commit 6dd692b945fc8599a4c7db22854d19c9b27d0d4c
Author: jkrcal <jkrcal@chromium.org>
Date: Thu Mar 02 12:49:19 2017

[Remote suggestions] Move all decisions to fetch to the scheduler

This change will clarify responsibilities between the scheduler and the
provider. On top of that, it eliminates the need to fetch snippets upon
creating the provider (which is dangerous w.r.t. fetches in unexpected
situations).

This change needs the new types of notifications from the provider to
the scheduler:
 - suggestions have been cleared (we should fetch on any later trigger),
 - history has been cleared (we should NOT fetch for a while).

Thus, the provider is now given a pointer to the scheduler interface.
(the interface now mixes internal and external signals but I think it is
this way easier to understand then with two separate interfaces).

BUG= 694324 

Review-Url: https://codereview.chromium.org/2702223004
Cr-Commit-Position: refs/heads/master@{#454240}

[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/chrome/browser/ntp_snippets/content_suggestions_service_factory.cc
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/content_suggestions_service.h
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/remote_suggestions_provider.h
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/remote_suggestions_provider_impl.cc
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/remote_suggestions_provider_impl.h
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/remote_suggestions_provider_impl_unittest.cc
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/remote_suggestions_scheduler.h
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/scheduling_remote_suggestions_provider.cc
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/scheduling_remote_suggestions_provider.h
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/components/ntp_snippets/remote/scheduling_remote_suggestions_provider_unittest.cc
[modify] https://crrev.com/6dd692b945fc8599a4c7db22854d19c9b27d0d4c/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc