[NTP Snippets] Refactor background scheduling for remote suggestions

components/ntp_snippets/content_suggestions_provider.h

Index: components/ntp_snippets/content_suggestions_provider.h
diff --git a/components/ntp_snippets/content_suggestions_provider.h b/components/ntp_snippets/content_suggestions_provider.h
index 8d941943475b434a3da0a0d90691e2cd097b4d4a..9e6cec9f339eb35c4ca95e8782c259213556235e 100644
--- a/components/ntp_snippets/content_suggestions_provider.h
+++ b/components/ntp_snippets/content_suggestions_provider.h
@@ -104,6 +104,13 @@ class ContentSuggestionsProvider {
                      const std::set<std::string>& known_suggestion_ids,
                      const FetchDoneCallback& callback) = 0;
 
+  // Reloads suggestions from all categories. Makes sense to call only after

[tschumann, 2016/12/15 19:27:00]

Can we find a better name for this method? To me it conveys pretty much no
semantics.
I find this comment confusing, why doesn't it make sense to call if no cards are
dismissed? It would still fetch new ones, right?

Isn't this just a FetchForAllCategories() functionality?

[jkrcal, 2016/12/19 09:40:24]

Removed the comment. 

As regards naming, this is a mess :) It is kind-of FetchForAllCategories but it
has a different API so I did not want to name the function analogously. Fetch
has fetch-and-return-by-callback semantics (and has not a clear semantics about
whether the additional suggestions should be cached in the provider). This is
fetch-for-all-and-notify-the-observer semantics.

Markus is about to clean things up a bit so this function may become redundant
and get renamed.

Do you feel strongly about some name?

+  // some suggestions have been dismissed. The provider may fill in the vacant
+  // space by new suggestions that haven't been included previously due to space
+  // limits. If this happens, the observer must be notified via
+  // OnNewSuggestions();
+  virtual void ReloadSuggestions() {}

[tschumann, 2016/12/15 19:27:00]

hm... we should make this pure virtual -- add a TODO()?

[jkrcal, 2016/12/19 09:40:24]

Done.

+
   // Removes history from the specified time range where the URL matches the
   // |filter|. The data removed depends on the provider. Note that the
   // data outside the time range may be deleted, for example suggestions, which