[Sync] Support open tabs experiment enabling before sync setup completion.

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 468 matching lines @@
 
     // The timer used to periodically call SaveChanges.
     base::RepeatingTimer<Core> save_changes_timer_;
 
     // The top-level syncapi entry point.  Lives on the sync thread.
     scoped_ptr<sync_api::SyncManager> sync_manager_;
 
     DISALLOW_COPY_AND_ASSIGN(Core);
   };
 
+  // Checks if we have received a notice to turn on experimental datatypes
+  // (via the nigori node) and informs the frontend if that is the case.
+  // Note: it is illegal to call this before the backend is initialized.
+  void AddExperimentalTypes();
+
   // InitializationComplete passes through the SyncBackendHost to forward
   // on to |frontend_|, and so that tests can intercept here if they need to
   // set up initial conditions.
   virtual void HandleInitializationCompletedOnFrontendLoop(
       const WeakHandle<JsBackend>& js_backend,
       bool success);
 
   // Called to finish the job of ConfigureDataTypes once the syncer is in
   // configuration mode.
   void FinishConfigureDataTypesOnFrontendLoop();
@@ skipping 78 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_