Implement ClearHistory for all ntp_snippets providers

components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc

 // 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.
 
 #include "components/ntp_snippets/offline_pages/offline_page_suggestions_provider.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/guid.h"
@@ skipping 136 matching lines @@
   // TODO(pke): Fetch proper thumbnail from OfflinePageModel once it's available
   // there.
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE, base::Bind(callback, gfx::Image()));
 }
 
 void OfflinePageSuggestionsProvider::ClearHistory(
     base::Time begin,
     base::Time end,
     const base::Callback<bool(const GURL& url)>& filter) {
-  // TODO(vitaliii): Implement. See crbug.com/641321.
+  ClearDismissedSuggestionsForDebugging(recent_tabs_category_);
+  ClearDismissedSuggestionsForDebugging(downloads_category_);
+  FetchOfflinePages();
 }
 
 void OfflinePageSuggestionsProvider::ClearCachedSuggestions(Category category) {
   // Ignored.
 }
 
 void OfflinePageSuggestionsProvider::GetDismissedSuggestionsForDebugging(
     Category category,
     const DismissedSuggestionsCallback& callback) {
   offline_page_model_->GetAllPages(
@@ skipping 215 matching lines @@
 void OfflinePageSuggestionsProvider::StoreDismissedIDsToPrefs(
     Category category,
     const std::set<std::string>& dismissed_ids) {
   base::ListValue list;
   for (const std::string& dismissed_id : dismissed_ids)
     list.AppendString(dismissed_id);
   pref_service_->Set(GetDismissedPref(category), list);
 }
 
 }  // namespace ntp_snippets