[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc

Index: components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc
diff --git a/components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc b/components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc
index 3c1b0e3e58017d788e065c94326f0ccf79613398..b9bb8da8cded9206a931d693f6dec38860861b08 100644
--- a/components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc
+++ b/components/ntp_snippets/offline_pages/offline_page_suggestions_provider.cc
@@ -5,6 +5,7 @@
 #include "components/ntp_snippets/offline_pages/offline_page_suggestions_provider.h"
 
 #include <algorithm>
+#include <utility>
 
 #include "base/bind.h"
 #include "base/guid.h"
@@ -14,6 +15,7 @@
 #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"
@@ -370,25 +372,15 @@ std::string OfflinePageSuggestionsProvider::GetDismissedPref(
 
 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