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..9389d6459f6d0b76047c5fc6e1c2ceef94671675 100644
--- a/chrome/browser/prefs/pref_model_associator.cc
+++ b/chrome/browser/prefs/pref_model_associator.cc
@@ -48,6 +48,42 @@ sync_pb::PreferenceSpecifics* GetMutableSpecifics(
   }
 }
 
+// List of migrated preference name pairs. If a preference is migrated
+// (meaning renamed) adding the old and new preference names here will ensure
+// that the sync engine knows how to deal with the synced values coming in
+// with the old name. Preference migration itself doesn't happen here. It may
+// happen in session_startup_pref.cc.
+const struct MigratedPreferences {
+  const char* const old_name;
+  const char* const new_name;
+} kMigratedPreferences[] = {
+  { prefs::kURLsToRestoreOnStartupOld, prefs::kURLsToRestoreOnStartup },
+};
+
+std::string GetOldMigratedPreferenceName(const char* preference_name) {
+  for (size_t i = 0; i < arraysize(kMigratedPreferences); ++i) {
+    if (!strcmp(kMigratedPreferences[i].new_name, preference_name))
+      return kMigratedPreferences[i].old_name;
+  }
+  return std::string();
+}
+
+std::string GetNewMigratedPreferenceName(const char* old_preference_name) {
+  for (size_t i = 0; i < arraysize(kMigratedPreferences); ++i) {
+    if (!strcmp(kMigratedPreferences[i].old_name, old_preference_name))
+      return kMigratedPreferences[i].new_name;
+  }
+  return std::string();
+}
+
+bool IsMigratedPreference(const char* preference_name) {
+  return !GetOldMigratedPreferenceName(preference_name).empty();
+}
+
+bool IsOldMigratedPreference(const char* old_preference_name) {
+  return !GetNewMigratedPreferenceName(old_preference_name).empty();
+}
+
 }  // namespace
 
 PrefModelAssociator::PrefModelAssociator(syncer::ModelType type)
@@ -78,7 +114,10 @@ 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() ||
+           (IsMigratedPreference(pref_name.c_str()) &&
+            preference.name() ==
+                GetOldMigratedPreferenceName(pref_name.c_str())));
 
     base::JSONReader reader;
     scoped_ptr<Value> sync_value(reader.ReadToValue(preference.value()));
@@ -119,6 +158,21 @@ void PrefModelAssociator::InitPrefAndAssociate(
             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 (IsMigratedPreference(pref_name.c_str())) {
+          if (!CreatePrefSyncData(
+                  GetOldMigratedPreferenceName(pref_name.c_str()),
+                  *new_value,
+                  &sync_data)) {
+            LOG(ERROR) << "Failed to update preference.";
+            return;
+          }
+          sync_changes->push_back(
+              syncer::SyncChange(FROM_HERE,
+                                 syncer::SyncChange::ACTION_UPDATE,
+                                 sync_data));
+        }
       }
     } else if (!sync_value->IsType(Value::TYPE_NULL)) {
       // Only a server value exists. Just set the local user value.
@@ -179,18 +233,26 @@ 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 (IsOldMigratedPreference(sync_pref_name.c_str())) {
+        // 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. Note that we will be merging any differences
+        // between the new and old values and sync'ing them back.
+        sync_pref_name = GetNewMigratedPreferenceName(sync_pref_name.c_str());
+      } 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 its datatype (therefore having
+        // 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 +287,10 @@ scoped_ptr<Value> PrefModelAssociator::MergePreference(
     const std::string& name,
     const Value& local_value,
     const Value& server_value) {
-  if (name == prefs::kURLsToRestoreOnStartup) {
+  // This function special cases preferences individually, so don't attempt
+  // to merge for all migrated values.
+  if (name == prefs::kURLsToRestoreOnStartup ||
+      name == prefs::kURLsToRestoreOnStartupOld) {
     return scoped_ptr<Value>(MergeListValues(local_value, server_value)).Pass();
   }
 
@@ -388,6 +453,13 @@ 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();
+    std::string new_name;
+    // We migrated this preference name, so do as if the name had not changed.
+    if (IsOldMigratedPreference(pref_name)) {
+      new_name = GetNewMigratedPreferenceName(pref_name);
+      pref_name = new_name.c_str();
+    }
+
     if (!IsPrefRegistered(pref_name))
       continue;
 
@@ -508,6 +580,21 @@ 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 (IsMigratedPreference(name.c_str())) {
+      if (!CreatePrefSyncData(GetOldMigratedPreferenceName(name.c_str()),
+                              *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 =