[Sync] Add support for enabling session sync remotely.

chrome/browser/sync/glue/sync_backend_host.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_
 #define CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 83 matching lines @@
   // encrypted using the accepted passphrase.
   virtual void OnPassphraseAccepted() = 0;
 
   virtual void OnEncryptionComplete(
       const syncable::ModelTypeSet& encrypted_types) = 0;
 
   // Called to perform migration of |types|.
   virtual void OnMigrationNeededForTypes(
       const syncable::ModelTypeSet& types) = 0;
 
+  // Inform the Frontend that new datatypes are available for registration.
+  virtual void OnDataTypesChanged(const syncable::ModelTypeSet& to_add) = 0;
+
  protected:
   // Don't delete through SyncFrontend interface.
   virtual ~SyncFrontend() {
   }
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncFrontend);
 };
 
 // A UI-thread safe API into the sync backend that "hosts" the top-level
 // syncapi element, the SyncManager, on its own thread. This class handles
@@ skipping 498 matching lines @@
 
   // UI-thread cache of the last SyncSessionSnapshot received from syncapi.
   scoped_ptr<sessions::SyncSessionSnapshot> last_snapshot_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHost);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_