Implement ClearHistory for all ntp_snippets providers

components/ntp_snippets/ntp_snippets_service.cc

 // Copyright 2015 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/ntp_snippets_service.h"
 
 #include <algorithm>
 #include <iterator>
 #include <utility>
 
@@ skipping 321 matching lines @@
   database_->LoadImage(
       snippet_id,
       base::Bind(&NTPSnippetsService::OnSnippetImageFetchedFromDatabase,
                  base::Unretained(this), callback, snippet_id));
 }
 
 void NTPSnippetsService::ClearHistory(
     base::Time begin,
     base::Time end,
     const base::Callback<bool(const GURL& url)>& filter) {
-  // TODO(vitaliii): Implement. See crbug.com/641321.
+  // Both time range and the filter are ignored and all suggestions are removed,
+  // because it is not known which history entries were used for the suggestions
+  // personalization.
+  if (!ready())
+    nuke_after_load_ = true;
+  else
+    NukeAllSnippets();
 }
 
 void NTPSnippetsService::ClearCachedSuggestions(Category category) {
   DCHECK_EQ(category, provided_category_);
   if (!initialized())
     return;
 
   if (snippets_.empty())
     return;
 
@@ skipping 546 matching lines @@
 void NTPSnippetsService::UpdateCategoryStatus(CategoryStatus status) {
   if (status == category_status_)
     return;
 
   category_status_ = status;
   observer()->OnCategoryStatusChanged(this, provided_category_,
                                       category_status_);
 }
 
 }  // namespace ntp_snippets