Add ClearHistory() to ContentSuggestionsService and its providers

components/ntp_snippets/content_suggestions_service.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_SERVICE_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_SERVICE_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 102 matching lines @@
 
   // Observer accessors.
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
   // Registers a new ContentSuggestionsProvider. It must be ensured that at most
   // one provider is registered for every category and that this method is
   // called only once per provider.
   void RegisterProvider(std::unique_ptr<ContentSuggestionsProvider> provider);
 
+  // Removes history from all providers, for example dismissed suggestions.
+  void ClearHistory();
+
   // Removes all suggestions from all caches or internal stores in all
   // providers. See |ClearCachedSuggestions|.
   void ClearAllCachedSuggestions();
 
   // Removes all suggestions of the given |category| from all caches or internal
   // stores in the service and the corresponding provider. It does, however, not
   // remove any suggestions from the provider's sources, so if its configuration
   // hasn't changed, it might return the same results when it fetches the next
   // time. In particular, calling this method will not mark any suggestions as
   // dismissed.
@@ skipping 96 matching lines @@
   // background fetching and debugging calls to it. If the NTPSnippetsService is
   // loaded, it is also present in |providers_|, otherwise this is a nullptr.
   NTPSnippetsService* ntp_snippets_service_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentSuggestionsService);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_SERVICE_H_