[Sync] Add support for enabling session sync remotely.

chrome/browser/sync/profile_sync_service.h

Index: chrome/browser/sync/profile_sync_service.h
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index b39cacf6b7e16468bb41cf4852fc394d8ae1e821..0af7081470d24f4fc938ef66497ecb372cc6fb5c 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -207,6 +207,8 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
       const syncable::ModelTypeSet& encrypted_types) OVERRIDE;
   virtual void OnMigrationNeededForTypes(
       const syncable::ModelTypeSet& types) OVERRIDE;
+  virtual void OnDataTypesChanged(
+      const syncable::ModelTypeSet& to_add) OVERRIDE;
 
   void OnClearServerDataTimeout();
 
@@ -551,6 +553,14 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
 
   static const char* GetPrefNameForDataType(syncable::ModelType data_type);
 
+  // About-flags experiment names for datatypes that aren't enabled by default
+  // yet.
+  static std::string GetExperimentNameForDataType(
+      syncable::ModelType data_type);
+
+  // Create and register a new datatype controller.
+  void RegisterNewDataType(syncable::ModelType data_type);
+
   // Time at which we begin an attempt a GAIA authorization.
   base::TimeTicks auth_start_time_;