[Sync] Initial implementation of foreign sessions suggestions provider.

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 <utility>
 
 #include "base/bind.h"
 #include "base/guid.h"
 #include "base/location.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/values.h"
 #include "components/ntp_snippets/pref_names.h"
+#include "components/ntp_snippets/pref_util.h"
 #include "components/offline_pages/client_namespace_constants.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
 #include "grit/components_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/image/image.h"
 
 using offline_pages::MultipleOfflinePageItemResult;
 using offline_pages::OfflinePageModel;
 using offline_pages::OfflinePageItem;
@@ skipping 336 matching lines @@
   if (category == recent_tabs_category_)
     return prefs::kDismissedRecentOfflineTabSuggestions;
   if (category == downloads_category_)
     return prefs::kDismissedDownloadSuggestions;
   NOTREACHED() << "Unknown category " << category.id();
   return std::string();
 }
 
 std::set<std::string> OfflinePageSuggestionsProvider::ReadDismissedIDsFromPrefs(
     Category category) const {
-  std::set<std::string> dismissed_ids;
-  const base::ListValue* list =
-      pref_service_->GetList(GetDismissedPref(category));
-  for (const std::unique_ptr<base::Value>& value : *list) {
-    std::string dismissed_id;
-    bool success = value->GetAsString(&dismissed_id);
-    DCHECK(success) << "Failed to parse dismissed offline page ID from prefs";
-    dismissed_ids.insert(dismissed_id);
-  }
-  return dismissed_ids;
+  return prefs::ReadDismissedIDsFromPrefs(*pref_service_,
+                                          GetDismissedPref(category));
 }
 
 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);
+  prefs::StoreDismissedIDsToPrefs(pref_service_, GetDismissedPref(category),
+                                  dismissed_ids);
 }
 
 }  // namespace ntp_snippets