Migrate startup URLs pref.

chrome/browser/prefs/pref_model_associator.cc

Index: chrome/browser/prefs/pref_model_associator.cc
diff --git a/chrome/browser/prefs/pref_model_associator.cc b/chrome/browser/prefs/pref_model_associator.cc
index 28759a10b6919b681ac7fcea46e5fc8227e7fc00..7dba18ed6ea17d2d736acbafb7510d2b6231622c 100644
--- a/chrome/browser/prefs/pref_model_associator.cc
+++ b/chrome/browser/prefs/pref_model_associator.cc
@@ -78,7 +78,9 @@ void PrefModelAssociator::InitPrefAndAssociate(
 
   if (sync_pref.IsValid()) {
     const sync_pb::PreferenceSpecifics& preference = GetSpecifics(sync_pref);
-    DCHECK_EQ(pref_name, preference.name());
+    DCHECK(pref_name == preference.name() ||
+           (pref_name == prefs::kURLsToRestoreOnStartup &&
+            preference.name() == prefs::kURLsToRestoreOnStartupOld));
 
     base::JSONReader reader;
     scoped_ptr<Value> sync_value(reader.ReadToValue(preference.value()));
@@ -179,18 +181,25 @@ syncer::SyncMergeResult PrefModelAssociator::MergeDataAndStartSyncing(
     DCHECK_EQ(type_, sync_iter->GetDataType());
 
     const sync_pb::PreferenceSpecifics& preference = GetSpecifics(*sync_iter);
-    const std::string& sync_pref_name = preference.name();
+    std::string sync_pref_name = preference.name();
 
     if (remaining_preferences.count(sync_pref_name) == 0) {
-      // We're not syncing this preference locally, ignore the sync data.
-      // TODO(zea): Eventually we want to be able to have the syncable service
-      // reconstruct all sync data for it's datatype (therefore having
-      // GetAllSyncData be a complete representation). We should store this data
-      // somewhere, even if we don't use it.
-      continue;
+      if (sync_pref_name == prefs::kURLsToRestoreOnStartupOld) {
+        // This old pref name is not syncable locally anymore but we accept
+        // changes from other Chrome installs of previous versions and migrate
+        // them to the new name.
+        sync_pref_name = prefs::kURLsToRestoreOnStartup;

[Nicolas Zea, 2013/10/04 17:45:01]

Maybe mention that we'll be merging any difference between the new and old
values and syncing them back?

[MAD, 2013/10/04 19:31:22]

Done.

+      } else {
+        // We're not syncing this preference locally, ignore the sync data.
+        // TODO(zea): Eventually we want to be able to have the syncable service
+        // reconstruct all sync data for it's datatype (therefore having

[grt (UTC plus 2), 2013/10/04 18:24:07]

it's -> its

[MAD, 2013/10/04 19:31:22]

Done.

+        // GetAllSyncData be a complete representation). We should store this
+        // data somewhere, even if we don't use it.
+        continue;
+      }
+    } else {
+      remaining_preferences.erase(sync_pref_name);
     }
-
-    remaining_preferences.erase(sync_pref_name);
     InitPrefAndAssociate(*sync_iter, sync_pref_name, &new_changes);
   }
 
@@ -225,7 +234,8 @@ scoped_ptr<Value> PrefModelAssociator::MergePreference(
     const std::string& name,
     const Value& local_value,
     const Value& server_value) {
-  if (name == prefs::kURLsToRestoreOnStartup) {
+  if (name == prefs::kURLsToRestoreOnStartup ||
+      name == prefs::kURLsToRestoreOnStartupOld) {
     return scoped_ptr<Value>(MergeListValues(local_value, server_value)).Pass();
   }
 
@@ -388,7 +398,10 @@ syncer::SyncError PrefModelAssociator::ProcessSyncChanges(
     // Windows client, the Windows client does not support
     // kConfirmToQuitEnabled. Ignore updates from these preferences.
     const char* pref_name = name.c_str();
-    if (!IsPrefRegistered(pref_name))
+    // We migrated this preference name, so do as if the name had not changed.
+    if (name == prefs::kURLsToRestoreOnStartupOld)
+      pref_name = prefs::kURLsToRestoreOnStartup;
+    else if (!IsPrefRegistered(pref_name))
       continue;
 
     const PrefService::Preference* pref =
@@ -508,6 +521,22 @@ void PrefModelAssociator::ProcessPrefChange(const std::string& name) {
         syncer::SyncChange(FROM_HERE,
                            syncer::SyncChange::ACTION_UPDATE,
                            sync_data));
+    // This preference has been migrated from an old version that must be kept
+    // in sync on older versions of Chrome.
+    if (name == prefs::kURLsToRestoreOnStartup) {
+      syncer::SyncData sync_data;
+      if (!CreatePrefSyncData(prefs::kURLsToRestoreOnStartupOld,
+                              *preference->GetValue(),
+                              &sync_data)) {
+        LOG(ERROR) << "Failed to update preference.";
+        return;
+      }
+
+      changes.push_back(
+          syncer::SyncChange(FROM_HERE,
+                             syncer::SyncChange::ACTION_UPDATE,
+                             sync_data));
+    }
   }
 
   syncer::SyncError error =