Refactor preference syncing.

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 688a4fa18b3f1e425e26d3911fbb64e71805fc16..a731fac067df3133c8d45f92f523e966ee41bcaf 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -505,6 +505,9 @@ void SyncBackendHost::ActivateDataType(
   // processors so it can receive updates.
   DCHECK_EQ(processors_.count(type), 0U);
   processors_[type] = change_processor;
+
+  // Start the change processor.
+  change_processor->Start(profile_, GetUserShare());
 }
 
 void SyncBackendHost::DeactivateDataType(
@@ -513,6 +516,8 @@ void SyncBackendHost::DeactivateDataType(
   base::AutoLock lock(registrar_lock_);
   registrar_.routing_info.erase(data_type_controller->type());
 
+  // Stop the change processor and remove it from the list of processors.
+  change_processor->Stop();
   std::map<syncable::ModelType, ChangeProcessor*>::size_type erased =
       processors_.erase(data_type_controller->type());
   DCHECK_EQ(erased, 1U);