[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/pref_names.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 <memory>
+
+#include "base/values.h"
 #include "components/ntp_snippets/pref_names.h"
+#include "components/prefs/pref_service.h"
 
 namespace ntp_snippets {
 namespace prefs {
 
 const char kEnableSnippets[] = "ntp_snippets.enable";
 
 const char kSnippetHosts[] = "ntp_snippets.hosts";
 
 const char kSnippetFetcherRequestCount[] =
     "ntp.request_throttler.suggestion_fetcher.count";
 const char kSnippetFetcherInteractiveRequestCount[] =
     "ntp.request_throttler.suggestion_fetcher.interactive_count";
 const char kSnippetFetcherRequestsDay[] =
     "ntp.request_throttler.suggestion_fetcher.day";
 
 const char kSnippetThumbnailsRequestCount[] =
     "ntp.request_throttler.suggestion_thumbnails.count";
 const char kSnippetThumbnailsInteractiveRequestCount[] =
     "ntp.request_throttler.suggestion_thumbnails.interactive_count";
 const char kSnippetThumbnailsRequestsDay[] =
     "ntp.request_throttler.suggestion_thumbnails.day";
 
 const char kDismissedRecentOfflineTabSuggestions[] =
     "ntp_suggestions.offline_pages.recent_tabs.dismissed_ids";
 const char kDismissedDownloadSuggestions[] =
     "ntp_suggestions.offline_pages.downloads.dismissed_ids";
+const char kDismissedForeignSessionsSuggestions[] =
+    "ntp_suggestoin.foreign_sessions.dismissed_ids";
 
 const char kBookmarksFirstM54Start[] =
     "ntp_suggestions.bookmarks.first_M54_start";
 
+std::set<std::string> ReadDismissedIDsFromPrefs(const std::string& pref_name,
+                                                PrefService* pref_service) {
+  std::set<std::string> dismissed_ids;
+  const base::ListValue* list = pref_service->GetList(pref_name);
+  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 id from prefs param "
+                    << pref_name << " into string.";
+    dismissed_ids.insert(dismissed_id);
+  }
+  return dismissed_ids;
+}
+
+void StoreDismissedIDsToPrefs(const std::string& pref_name,
+                              const std::set<std::string>& dismissed_ids,
+                              PrefService* pref_service) {
+  base::ListValue list;
+  for (const std::string& dismissed_id : dismissed_ids) {
+    list.AppendString(dismissed_id);
+  }
+  pref_service->Set(pref_name, list);
+}
+
 }  // namespace prefs
 }  // namespace ntp_snippets