No longer keep a lingering reference to TypedUrlDataTypeController after PSS exits

chrome/browser/sync/glue/non_frontend_data_type_controller.h

Index: chrome/browser/sync/glue/non_frontend_data_type_controller.h
diff --git a/chrome/browser/sync/glue/non_frontend_data_type_controller.h b/chrome/browser/sync/glue/non_frontend_data_type_controller.h
index 9d9d6092fa60ce2ac8c8d62999788e2cccdc09b6..f9245632271cd2aa3930023ff5db308fb5296247 100644
--- a/chrome/browser/sync/glue/non_frontend_data_type_controller.h
+++ b/chrome/browser/sync/glue/non_frontend_data_type_controller.h
@@ -78,6 +78,9 @@ class NonFrontendDataTypeController : public DataTypeController {
   // Posts the given task to the backend thread, i.e. the thread the
   // datatype lives on.  Return value: True if task posted successfully,
   // false otherwise.
+  // NOTE: The StopAssociationAsync() implementation relies on the fact that
+  // implementations of this API do not hold any references to the DTC while
+  // the task is executing. See http://crbug.com/127706.
   virtual bool PostTaskOnBackendThread(
       const tracked_objects::Location& from_here,
       const base::Closure& task) = 0;
@@ -176,10 +179,6 @@ class NonFrontendDataTypeController : public DataTypeController {
   bool abort_association_;
   base::WaitableEvent abort_association_complete_;
 
-  // Barrier to ensure that the datatype has been stopped on the DB thread
-  // from the UI thread.
-  base::WaitableEvent datatype_stopped_;
-
   // This is added for debugging purpose.
   // TODO(lipalani): Remove this after debugging.
   base::WaitableEvent start_association_called_;