Revert "Revert 142517 - [Sync] Refactor sync configuration logic."

chrome/browser/sync/glue/sync_backend_host.cc

Index: chrome/browser/sync/glue/sync_backend_host.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host.cc b/chrome/browser/sync/glue/sync_backend_host.cc
index 963ccaba599e2d8c73ee53f85c015595c5405c9f..84f98cddb831bd2d59cb69fbc69a78771c13e96a 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -126,10 +126,6 @@ class SyncBackendHost::Core
   // initialization and authentication).
   void DoStartSyncing(const syncer::ModelSafeRoutingInfo& routing_info);
 
-  // Called to cleanup disabled types.
-  void DoRequestCleanupDisabledTypes(
-      const syncer::ModelSafeRoutingInfo& routing_info);
-
   // Called to set the passphrase for encryption.
   void DoSetEncryptionPassphrase(const std::string& passphrase,
                                  bool is_explicit);
@@ -159,14 +155,18 @@ class SyncBackendHost::Core
   void DoStopSyncManagerForShutdown(const base::Closure& closure);
   void DoShutdown(bool stopping_sync);
 
-  virtual void DoRequestConfig(
-      const syncer::ModelSafeRoutingInfo& routing_info,
+  // Configuration methods that must execute on sync loop.
+  void DoConfigureSyncer(
+      syncer::ConfigureReason reason,
       syncer::ModelTypeSet types_to_config,
-      syncer::ConfigureReason reason);
-
-  // Start the configuration mode.  |callback| is called on the sync
-  // thread.
-  virtual void DoStartConfiguration(const base::Closure& callback);
+      const syncer::ModelSafeRoutingInfo routing_info,
+      const base::Callback<void(syncer::ModelTypeSet)>& ready_task,
+      const base::Closure& retry_callback);
+  void DoFinishConfigureDataTypes(
+      syncer::ModelTypeSet types_to_config,
+      const base::Callback<void(syncer::ModelTypeSet)>& ready_task);
+  void DoRetryConfiguration(
+      const base::Closure& retry_callback);
 
   // Set the base request context to use when making HTTP calls.
   // This method will add a reference to the context to persist it
@@ -179,9 +179,6 @@ class SyncBackendHost::Core
   // sync databases), as well as shutdown when you're no longer syncing.
   void DeleteSyncDataFolder();
 
-  // A callback from the SyncerThread when it is safe to continue config.
-  void FinishConfigureDataTypes();
-
  private:
   friend class base::RefCountedThreadSafe<SyncBackendHost::Core>;
   friend class SyncBackendHostForProfileSyncTest;
@@ -355,9 +352,10 @@ std::string MakeUserAgentForSyncApi() {
   return user_agent;
 }
 
-syncer::HttpPostProviderFactory* MakeHttpBridgeFactory(
+scoped_ptr<syncer::HttpPostProviderFactory> MakeHttpBridgeFactory(
     const scoped_refptr<net::URLRequestContextGetter>& getter) {
-  return new syncer::HttpBridgeFactory(getter, MakeUserAgentForSyncApi());
+  return scoped_ptr<syncer::HttpPostProviderFactory>(
+      new syncer::HttpBridgeFactory(getter, MakeUserAgentForSyncApi()));
 }
 
 }  // namespace
@@ -369,10 +367,11 @@ void SyncBackendHost::Initialize(
     syncer::ModelTypeSet initial_types,
     const SyncCredentials& credentials,
     bool delete_sync_data_folder,
+    syncer::SyncManagerFactory* sync_manager_factory,
     syncer::UnrecoverableErrorHandler* unrecoverable_error_handler,
     syncer::ReportUnrecoverableErrorFunction
         report_unrecoverable_error_function) {
-  if (!sync_thread_.Start())
+  if (!StartSyncThread())
     return;
 
   frontend_ = frontend;
@@ -407,6 +406,7 @@ void SyncBackendHost::Initialize(
       credentials,
       &chrome_sync_notification_bridge_,
       &sync_notifier_factory_,
+      sync_manager_factory,
       delete_sync_data_folder,
       sync_prefs_->GetEncryptionBootstrapToken(),
       syncer::SyncManager::NON_TEST,
@@ -589,8 +589,8 @@ void SyncBackendHost::ConfigureDataTypes(
     syncer::ModelTypeSet types_to_add,
     syncer::ModelTypeSet types_to_remove,
     NigoriState nigori_state,
-    base::Callback<void(syncer::ModelTypeSet)> ready_task,
-    base::Callback<void()> retry_callback) {
+    const base::Callback<void(syncer::ModelTypeSet)>& ready_task,
+    const base::Callback<void()>& retry_callback) {
   syncer::ModelTypeSet types_to_add_with_nigori = types_to_add;
   syncer::ModelTypeSet types_to_remove_with_nigori = types_to_remove;
   if (nigori_state == WITH_NIGORI) {
@@ -600,44 +600,56 @@ void SyncBackendHost::ConfigureDataTypes(
     types_to_add_with_nigori.Remove(syncer::NIGORI);
     types_to_remove_with_nigori.Put(syncer::NIGORI);
   }
-  // Only one configure is allowed at a time.
-  DCHECK(!pending_config_mode_state_.get());
-  DCHECK(!pending_download_state_.get());
+  // Only one configure is allowed at a time (DataTypeManager handles user
+  // changes that happen while the syncer is reconfiguring, and will only
+  // trigger another call to ConfigureDataTypes once the current reconfiguration
+  // completes).
   DCHECK_GT(initialization_state_, NOT_INITIALIZED);
 
-  pending_config_mode_state_.reset(new PendingConfigureDataTypesState());
-  pending_config_mode_state_->ready_task = ready_task;
-  pending_config_mode_state_->types_to_add = types_to_add_with_nigori;
-  pending_config_mode_state_->added_types =
-      registrar_->ConfigureDataTypes(types_to_add_with_nigori,
-                                     types_to_remove_with_nigori);
-  pending_config_mode_state_->reason = reason;
-  pending_config_mode_state_->retry_callback = retry_callback;
-
-  // Cleanup disabled types before starting configuration so that
-  // callers can assume that the data types are cleaned up once
-  // configuration is done.
-  if (!types_to_remove_with_nigori.Empty()) {
-    syncer::ModelSafeRoutingInfo routing_info;
-    registrar_->GetModelSafeRoutingInfo(&routing_info);
-    sync_thread_.message_loop()->PostTask(
-        FROM_HERE,
-        base::Bind(&SyncBackendHost::Core::DoRequestCleanupDisabledTypes,
-                   core_.get(),
-                   routing_info));
-  }
-
-  StartConfiguration(
-      base::Bind(&SyncBackendHost::Core::FinishConfigureDataTypes,
-                 core_.get()));
-}
-
-void SyncBackendHost::StartConfiguration(const base::Closure& callback) {
-  // Put syncer in the config mode. DTM will put us in normal mode once it is
-  // done. This is to ensure we dont do a normal sync when we are doing model
-  // association.
-  sync_thread_.message_loop()->PostTask(FROM_HERE, base::Bind(
-      &SyncBackendHost::Core::DoStartConfiguration, core_.get(), callback));
+  // The new set of enabled types is types_to_add_with_nigori + the
+  // previously enabled types (on restart, the preferred types are already
+  // enabled) - types_to_remove_with_nigori. After reconfiguring the registrar,
+  // the new routing info will reflect the set of enabled types.
+  syncer::ModelSafeRoutingInfo routing_info;
+  registrar_->ConfigureDataTypes(types_to_add_with_nigori,
+                                 types_to_remove_with_nigori);
+  registrar_->GetModelSafeRoutingInfo(&routing_info);
+  const syncer::ModelTypeSet enabled_types =
+      GetRoutingInfoTypes(routing_info);
+
+  // Figure out which types need to actually be downloaded. We pass those on
+  // to the syncer while it's in configuration mode so that they can be
+  // downloaded before we perform association. Once we switch to normal mode
+  // downloads will get applied normally and hit the datatype's change
+  // processor.
+  // A datatype is in need of downloading if any of the following are true:
+  // 1. it's enabled and initial_sync_ended is false (initial_sync_ended is
+  //    set after applying updates, and hence is a more conservative measure
+  //    than having a non-empty progress marker, which is set during
+  //    StoreTimestamps).
+  // 2. the type is NIGORI, and any other datatype is being downloaded (nigori
+  //    is always included if we download a datatype).
+  // TODO(sync): consider moving this logic onto the sync thread (perhaps
+  // as part of SyncManager::ConfigureSyncer).
+  syncer::ModelTypeSet initial_sync_ended_types =
+      core_->sync_manager()->InitialSyncEndedTypes();
+  initial_sync_ended_types.RetainAll(enabled_types);
+  syncer::ModelTypeSet types_to_config =
+      Difference(enabled_types, initial_sync_ended_types);
+  if (!types_to_config.Empty() && enabled_types.Has(syncer::NIGORI))
+    types_to_config.Put(syncer::NIGORI);
+
+  SDVLOG(1) << "Types "
+            << syncer::ModelTypeSetToString(types_to_config)
+            << " added; calling DoConfigureSyncer";
+  // TODO(zea): figure out how to bypass this call if no types are being
+  // configured and GetKey is not needed. For now we rely on determining the
+  // need for GetKey as part of the SyncManager::ConfigureSyncer logic.
+  RequestConfigureSyncer(reason,
+                         types_to_config,
+                         routing_info,
+                         ready_task,
+                         retry_callback);
 }
 
 void SyncBackendHost::EnableEncryptEverything() {
@@ -703,159 +715,58 @@ void SyncBackendHost::GetModelSafeRoutingInfo(
   }
 }
 
+bool SyncBackendHost::StartSyncThread() {
+  if (!sync_thread_.IsRunning())
+    return sync_thread_.Start();
+  return true;
+}
+
 void SyncBackendHost::InitCore(const DoInitializeOptions& options) {
   sync_thread_.message_loop()->PostTask(FROM_HERE,
       base::Bind(&SyncBackendHost::Core::DoInitialize, core_.get(), options));
 }
 
-void SyncBackendHost::HandleSyncCycleCompletedOnFrontendLoop(
-    const SyncSessionSnapshot& snapshot) {
-  if (!frontend_)
-    return;
-  DCHECK_EQ(MessageLoop::current(), frontend_loop_);
-
-  last_snapshot_ = snapshot;
-
-  SDVLOG(1) << "Got snapshot " << snapshot.ToString();
-
-  const syncer::ModelTypeSet to_migrate =
-      snapshot.model_neutral_state().types_needing_local_migration;
-  if (!to_migrate.Empty())
-    frontend_->OnMigrationNeededForTypes(to_migrate);
-
-  // Process any changes to the datatypes we're syncing.
-  // TODO(sync): add support for removing types.
-  if (initialized())
-    AddExperimentalTypes();
-
-  // If we are waiting for a configuration change, check here to see
-  // if this sync cycle has initialized all of the types we've been
-  // waiting for.
-  if (pending_download_state_.get()) {
-    const syncer::ModelTypeSet types_to_add =
-        pending_download_state_->types_to_add;
-    const syncer::ModelTypeSet added_types =
-        pending_download_state_->added_types;
-    DCHECK(types_to_add.HasAll(added_types));
-    const syncer::ModelTypeSet initial_sync_ended =
-        snapshot.initial_sync_ended();
-    const syncer::ModelTypeSet failed_configuration_types =
-        Difference(added_types, initial_sync_ended);
-    SDVLOG(1)
-        << "Added types: "
-        << syncer::ModelTypeSetToString(added_types)
-        << ", configured types: "
-        << syncer::ModelTypeSetToString(initial_sync_ended)
-        << ", failed configuration types: "
-        << syncer::ModelTypeSetToString(failed_configuration_types);
-
-    if (!failed_configuration_types.Empty() &&
-        snapshot.retry_scheduled()) {
-      // Inform the caller that download failed but we are retrying.
-      if (!pending_download_state_->retry_in_progress) {
-        pending_download_state_->retry_callback.Run();
-        pending_download_state_->retry_in_progress = true;
-      }
-      // Nothing more to do.
-      return;
-    }
-
-    scoped_ptr<PendingConfigureDataTypesState> state(
-        pending_download_state_.release());
-    state->ready_task.Run(failed_configuration_types);
-
-    // Syncer did not report an error but did not download everything
-    // we requested either. So abort. The caller of the config will cleanup.
-    if (!failed_configuration_types.Empty())
-      return;
-  }
-
-  if (initialized())
-    frontend_->OnSyncCycleCompleted();
-}
-
-void SyncBackendHost::FinishConfigureDataTypesOnFrontendLoop() {
-  DCHECK_EQ(MessageLoop::current(), frontend_loop_);
-  // Nudge the syncer. This is necessary for both datatype addition/deletion.
-  //
-  // Deletions need a nudge in order to ensure the deletion occurs in a timely
-  // manner (see issue 56416).
-  //
-  // In the case of additions, on the next sync cycle, the syncer should
-  // notice that the routing info has changed and start the process of
-  // downloading updates for newly added data types.  Once this is
-  // complete, the configure_state_.ready_task_ is run via an
-  // OnInitializationComplete notification.
-
-  SDVLOG(1) << "Syncer in config mode. SBH executing "
-            << "FinishConfigureDataTypesOnFrontendLoop";
-
-  syncer::ModelSafeRoutingInfo routing_info;
-  registrar_->GetModelSafeRoutingInfo(&routing_info);
-  const syncer::ModelTypeSet enabled_types = GetRoutingInfoTypes(routing_info);
+void SyncBackendHost::RequestConfigureSyncer(
+    syncer::ConfigureReason reason,
+    syncer::ModelTypeSet types_to_config,
+    const syncer::ModelSafeRoutingInfo& routing_info,
+    const base::Callback<void(syncer::ModelTypeSet)>& ready_task,
+    const base::Closure& retry_callback) {
+  sync_thread_.message_loop()->PostTask(FROM_HERE,
+       base::Bind(&SyncBackendHost::Core::DoConfigureSyncer,
+                  core_.get(),
+                  reason,
+                  types_to_config,
+                  routing_info,
+                  ready_task,
+                  retry_callback));
+}
+
+void SyncBackendHost::FinishConfigureDataTypesOnFrontendLoop(
+    syncer::ModelTypeSet types_to_configure,
+    syncer::ModelTypeSet configured_types,
+    const base::Callback<void(syncer::ModelTypeSet)>& ready_task) {
+  const syncer::ModelTypeSet failed_configuration_types =
+      Difference(types_to_configure, configured_types);
+  SDVLOG(1)
+      << "Added types: "
+      << syncer::ModelTypeSetToString(types_to_configure)
+      << ", configured types: "
+      << syncer::ModelTypeSetToString(configured_types)
+      << ", failed configuration types: "
+      << syncer::ModelTypeSetToString(failed_configuration_types);
 
   // Update |chrome_sync_notification_bridge_|'s enabled types here as it has
   // to happen on the UI thread.
-  chrome_sync_notification_bridge_.UpdateEnabledTypes(enabled_types);
-
-  if (pending_config_mode_state_->added_types.Empty() &&
-      !core_->sync_manager()->InitialSyncEndedTypes().HasAll(enabled_types)) {
-
-    // TODO(tim): Log / UMA / count this somehow?
-    // Add only the types with empty progress markers. Note: it is possible
-    // that some types have their initial_sync_ended be false but with non
-    // empty progress marker. Which is ok as the rest of the changes would
-    // be downloaded on a regular nudge and initial_sync_ended should be set
-    // to true. However this is a very corner case. So it is not explicitly
-    // handled.
-    pending_config_mode_state_->added_types =
-        syncer::GetTypesWithEmptyProgressMarkerToken(enabled_types,
-                                                       GetUserShare());
-  }
-
-  // If we've added types, we always want to request a nudge/config (even if
-  // the initial sync is ended), in case we could not decrypt the data.
-  if (pending_config_mode_state_->added_types.Empty()) {
-    SDVLOG(1) << "No new types added; calling ready_task directly";
-    // No new types - just notify the caller that the types are available.
-    const syncer::ModelTypeSet failed_configuration_types;
-    pending_config_mode_state_->ready_task.Run(failed_configuration_types);
-  } else {
-    pending_download_state_.reset(pending_config_mode_state_.release());
-
-    // Always configure nigori if it's enabled.
-    syncer::ModelTypeSet types_to_config = pending_download_state_->added_types;
-    if (IsNigoriEnabled()) {
-      // Note: Nigori is the only type that gets added with a nonempty
-      // progress marker during config. If the server returns a migration
-      // error then we will go into unrecoverable error. We dont handle it
-      // explicitly because server might help us out here by not sending a
-      // migraiton error for nigori during config.
-      types_to_config.Put(syncer::NIGORI);
-    }
-    SDVLOG(1) << "Types "
-              << syncer::ModelTypeSetToString(types_to_config)
-              << " added; calling DoRequestConfig";
-    syncer::ModelSafeRoutingInfo routing_info;
-    registrar_->GetModelSafeRoutingInfo(&routing_info);
-    sync_thread_.message_loop()->PostTask(FROM_HERE,
-         base::Bind(&SyncBackendHost::Core::DoRequestConfig,
-                    core_.get(),
-                    routing_info,
-                    types_to_config,
-                    pending_download_state_->reason));
-  }
-
-  pending_config_mode_state_.reset();
+  chrome_sync_notification_bridge_.UpdateEnabledTypes(configured_types);
 
   // Notify SyncManager (especially the notification listener) about new types.
   sync_thread_.message_loop()->PostTask(FROM_HERE,
       base::Bind(&SyncBackendHost::Core::DoUpdateEnabledTypes, core_.get(),
-                 enabled_types));
-}
+                 configured_types));
 
-bool SyncBackendHost::IsDownloadingNigoriForTest() const {
-  return initialization_state_ == DOWNLOADING_NIGORI;
+  if (!ready_task.is_null())
+    ready_task.Run(failed_configuration_types);
 }
 
 SyncBackendHost::DoInitializeOptions::DoInitializeOptions(
@@ -870,6 +781,7 @@ SyncBackendHost::DoInitializeOptions::DoInitializeOptions(
     const syncer::SyncCredentials& credentials,
     ChromeSyncNotificationBridge* chrome_sync_notification_bridge,
     syncer::SyncNotifierFactory* sync_notifier_factory,
+    syncer::SyncManagerFactory* sync_manager_factory,
     bool delete_sync_data_folder,
     const std::string& restored_key_for_bootstrapping,
     syncer::SyncManager::TestingMode testing_mode,
@@ -887,6 +799,7 @@ SyncBackendHost::DoInitializeOptions::DoInitializeOptions(
       credentials(credentials),
       chrome_sync_notification_bridge(chrome_sync_notification_bridge),
       sync_notifier_factory(sync_notifier_factory),
+      sync_manager_factory(sync_manager_factory),
       delete_sync_data_folder(delete_sync_data_folder),
       restored_key_for_bootstrapping(restored_key_for_bootstrapping),
       testing_mode(testing_mode),
@@ -913,14 +826,6 @@ SyncBackendHost::Core::~Core() {
   DCHECK(!sync_loop_);
 }
 
-SyncBackendHost::PendingConfigureDataTypesState::
-PendingConfigureDataTypesState()
-    : reason(syncer::CONFIGURE_REASON_UNKNOWN),
-      retry_in_progress(false) {}
-
-SyncBackendHost::PendingConfigureDataTypesState::
-~PendingConfigureDataTypesState() {}
-
 void SyncBackendHost::Core::OnSyncCycleCompleted(
     const SyncSessionSnapshot& snapshot) {
   if (!sync_loop_)
@@ -1061,7 +966,7 @@ void SyncBackendHost::Core::DoInitialize(const DoInitializeOptions& options) {
   registrar_ = options.registrar;
   DCHECK(registrar_);
 
-  sync_manager_.reset(new syncer::SyncManager(name_));
+  sync_manager_ = options.sync_manager_factory->CreateSyncManager(name_);
   sync_manager_->AddObserver(this);
   success = sync_manager_->Init(
       sync_data_folder_path_,
@@ -1070,15 +975,15 @@ void SyncBackendHost::Core::DoInitialize(const DoInitializeOptions& options) {
       options.service_url.EffectiveIntPort(),
       options.service_url.SchemeIsSecure(),
       BrowserThread::GetBlockingPool(),
-      options.make_http_bridge_factory_fn.Run(),
+      options.make_http_bridge_factory_fn.Run().Pass(),
       options.routing_info,
       options.workers,
       options.extensions_activity_monitor,
       options.registrar /* as SyncManager::ChangeDelegate */,
       options.credentials,
-      new BridgedSyncNotifier(
+      scoped_ptr<syncer::SyncNotifier>(new BridgedSyncNotifier(
           options.chrome_sync_notification_bridge,
-          options.sync_notifier_factory->CreateSyncNotifier()),
+          options.sync_notifier_factory->CreateSyncNotifier())),
       options.restored_key_for_bootstrapping,
       options.testing_mode,
       &encryptor_,
@@ -1116,12 +1021,6 @@ void SyncBackendHost::Core::DoStartSyncing(
   sync_manager_->StartSyncingNormally(routing_info);
 }
 
-void SyncBackendHost::Core::DoRequestCleanupDisabledTypes(
-    const syncer::ModelSafeRoutingInfo& routing_info) {
-  DCHECK_EQ(MessageLoop::current(), sync_loop_);
-  sync_manager_->RequestCleanupDisabledTypes(routing_info);
-}
-
 void SyncBackendHost::Core::DoSetEncryptionPassphrase(
     const std::string& passphrase,
     bool is_explicit) {
@@ -1173,18 +1072,46 @@ void SyncBackendHost::Core::DoShutdown(bool sync_disabled) {
   host_.Reset();
 }
 
-void SyncBackendHost::Core::DoRequestConfig(
-    const syncer::ModelSafeRoutingInfo& routing_info,
+void SyncBackendHost::Core::DoConfigureSyncer(
+    syncer::ConfigureReason reason,
     syncer::ModelTypeSet types_to_config,
-    syncer::ConfigureReason reason) {
+    const syncer::ModelSafeRoutingInfo routing_info,
+    const base::Callback<void(syncer::ModelTypeSet)>& ready_task,
+    const base::Closure& retry_callback) {
   DCHECK_EQ(MessageLoop::current(), sync_loop_);
-  sync_manager_->RequestConfig(routing_info, types_to_config, reason);
+  sync_manager_->ConfigureSyncer(
+      reason,
+      types_to_config,
+      routing_info,
+      base::Bind(&SyncBackendHost::Core::DoFinishConfigureDataTypes,
+                 this,
+                 types_to_config,
+                 ready_task),
+      base::Bind(&SyncBackendHost::Core::DoRetryConfiguration,
+                 this,
+                 retry_callback));
 }
 
-void SyncBackendHost::Core::DoStartConfiguration(
-    const base::Closure& callback) {
+void SyncBackendHost::Core::DoFinishConfigureDataTypes(
+    syncer::ModelTypeSet types_to_config,
+    const base::Callback<void(syncer::ModelTypeSet)>& ready_task) {
   DCHECK_EQ(MessageLoop::current(), sync_loop_);
-  sync_manager_->StartConfigurationMode(callback);
+  syncer::ModelTypeSet configured_types =
+      sync_manager_->InitialSyncEndedTypes();
+  configured_types.RetainAll(types_to_config);
+  host_.Call(FROM_HERE,
+             &SyncBackendHost::FinishConfigureDataTypesOnFrontendLoop,
+             types_to_config,
+             configured_types,
+             ready_task);
+}
+
+void SyncBackendHost::Core::DoRetryConfiguration(
+    const base::Closure& retry_callback) {
+  DCHECK_EQ(MessageLoop::current(), sync_loop_);
+  host_.Call(FROM_HERE,
+             &SyncBackendHost::RetryConfigurationOnFrontendLoop,
+             retry_callback);
 }
 
 void SyncBackendHost::Core::DeleteSyncDataFolder() {
@@ -1195,13 +1122,6 @@ void SyncBackendHost::Core::DeleteSyncDataFolder() {
   }
 }
 
-void SyncBackendHost::Core::FinishConfigureDataTypes() {
-  DCHECK_EQ(MessageLoop::current(), sync_loop_);
-  host_.Call(
-      FROM_HERE,
-      &SyncBackendHost::FinishConfigureDataTypesOnFrontendLoop);
-}
-
 void SyncBackendHost::Core::StartSavingChanges() {
   // We may already be shut down.
   if (!sync_loop_)
@@ -1234,6 +1154,21 @@ void SyncBackendHost::OnNigoriDownloadRetry() {
   frontend_->OnSyncConfigureRetry();
 }
 
+namespace {
+
+syncer::ModelTypeSet GetPartiallySyncedTypes(
+      syncer::SyncManager* sync_manager) {
+  syncer::ModelTypeSet partially_synced_types =
+      syncer::ModelTypeSet::All();
+  partially_synced_types.RemoveAll(sync_manager->InitialSyncEndedTypes());
+  partially_synced_types.RemoveAll(
+      sync_manager->GetTypesWithEmptyProgressMarkerToken(
+          syncer::ModelTypeSet::All()));
+  return partially_synced_types;
+}
+
+}  // namespace
+
 void SyncBackendHost::HandleInitializationCompletedOnFrontendLoop(
     const syncer::WeakHandle<syncer::JsBackend>& js_backend, bool success) {
   DCHECK_NE(NOT_ATTEMPTED, initialization_state_);
@@ -1253,17 +1188,61 @@ void SyncBackendHost::HandleInitializationCompletedOnFrontendLoop(
     return;
   }
 
-  // If setup has completed, start off in DOWNLOADING_NIGORI so that
-  // we start off by refreshing nigori.
-  CHECK(sync_prefs_.get());
-  if (sync_prefs_->HasSyncSetupCompleted() &&
-      initialization_state_ < DOWNLOADING_NIGORI) {
-    initialization_state_ = DOWNLOADING_NIGORI;
-  }
-
   // Run initialization state machine.
   switch (initialization_state_) {
-    case NOT_INITIALIZED:
+    case NOT_INITIALIZED: {
+      NigoriState nigori_state;
+      syncer::ModelTypeSet partially_synced_types = GetPartiallySyncedTypes(
+          core_->sync_manager());
+
+      // Although it's possible for any type to be in a partially downloaded
+      // state, we only care about nigori as it's the only one we download
+      // before the backend is fully initialized. Other types will be
+      // re-downloaded at configuration time, at which point we can handle
+      // migrations and other events.
+      UMA_HISTOGRAM_COUNTS("Sync.PartiallySyncedTypes",
+                           partially_synced_types.Size());
+
+      if (partially_synced_types.Has(syncer::NIGORI)) {
+        // Configure without nigori to force it to be cleaned (
+        // SyncBackendRegistrar will remove nigori from routing info as part
+        // of the configuration).
+        nigori_state = WITHOUT_NIGORI;
+        initialization_state_ = CLEANING_NIGORI;
+      } else {
+        // Normal configuration. Will do nothing if the nigori is already
+        // downloaded and applied.
+        nigori_state = WITH_NIGORI;
+        initialization_state_ = DOWNLOADING_NIGORI;
+      }
+      ConfigureDataTypes(
+          syncer::CONFIGURE_REASON_NEW_CLIENT,
+          syncer::ModelTypeSet(),
+          syncer::ModelTypeSet(),
+          nigori_state,
+          // Calls back into this function.
+          base::Bind(
+              &SyncBackendHost::
+                  HandleNigoriConfigurationCompletedOnFrontendLoop,
+              weak_ptr_factory_.GetWeakPtr(), js_backend),
+          base::Bind(&SyncBackendHost::OnNigoriDownloadRetry,
+                     weak_ptr_factory_.GetWeakPtr()));
+      break;
+    }
+    case CLEANING_NIGORI: {
+      syncer::ModelTypeSet partially_synced_types = GetPartiallySyncedTypes(
+          core_->sync_manager());
+      if (partially_synced_types.Has(syncer::NIGORI)) {
+        // We apparently failed to clean the nigori somehow. Attempting
+        // to continue could lead to crashes (see bug 133219), so we fail
+        // gracefully instead by triggering an unrecoverable error.
+        LOG(ERROR) << "Failed to cleanup partial nigori.";
+        initialization_state_ = NOT_INITIALIZED;
+        frontend_->OnBackendInitialized(
+            syncer::WeakHandle<syncer::JsBackend>(), false);
+        return;
+      }
+
       initialization_state_ = DOWNLOADING_NIGORI;
       ConfigureDataTypes(
           syncer::CONFIGURE_REASON_NEW_CLIENT,
@@ -1278,6 +1257,7 @@ void SyncBackendHost::HandleInitializationCompletedOnFrontendLoop(
           base::Bind(&SyncBackendHost::OnNigoriDownloadRetry,
                      weak_ptr_factory_.GetWeakPtr()));
       break;
+    }
     case DOWNLOADING_NIGORI:
       initialization_state_ = REFRESHING_NIGORI;
       // Triggers OnEncryptedTypesChanged() and OnEncryptionComplete()
@@ -1301,6 +1281,36 @@ void SyncBackendHost::HandleInitializationCompletedOnFrontendLoop(
   }
 }
 
+void SyncBackendHost::HandleSyncCycleCompletedOnFrontendLoop(
+    const SyncSessionSnapshot& snapshot) {
+  if (!frontend_)
+    return;
+  DCHECK_EQ(MessageLoop::current(), frontend_loop_);
+
+  last_snapshot_ = snapshot;
+
+  SDVLOG(1) << "Got snapshot " << snapshot.ToString();
+
+  const syncer::ModelTypeSet to_migrate =
+      snapshot.model_neutral_state().types_needing_local_migration;
+  if (!to_migrate.Empty())
+    frontend_->OnMigrationNeededForTypes(to_migrate);
+
+  // Process any changes to the datatypes we're syncing.
+  // TODO(sync): add support for removing types.
+  if (initialized())
+    AddExperimentalTypes();
+
+  if (initialized())
+    frontend_->OnSyncCycleCompleted();
+}
+
+void SyncBackendHost::RetryConfigurationOnFrontendLoop(
+    const base::Closure& retry_callback) {
+  SDVLOG(1) << "Failed to complete configuration, informing of retry.";
+  retry_callback.Run();
+}
+
 void SyncBackendHost::PersistEncryptionBootstrapToken(
     const std::string& token) {
   CHECK(sync_prefs_.get());