Mojo C++ bindings: make SyncHandleRegistry a ref-counted object.

mojo/public/cpp/bindings/lib/sync_handle_watcher.h

Index: mojo/public/cpp/bindings/lib/sync_handle_watcher.h
diff --git a/mojo/public/cpp/bindings/lib/sync_handle_watcher.h b/mojo/public/cpp/bindings/lib/sync_handle_watcher.h
index 8d4fd5510a533bb5bb939a4ef261916acadba7f3..93d527bdc8358ac7032a2de7d9b8f603ebbfe23d 100644
--- a/mojo/public/cpp/bindings/lib/sync_handle_watcher.h
+++ b/mojo/public/cpp/bindings/lib/sync_handle_watcher.h
@@ -61,6 +61,8 @@ class SyncHandleWatcher {
   // If non-zero, |handle_| should be registered with SyncHandleRegistry.
   size_t register_request_count_;
 
+  scoped_refptr<SyncHandleRegistry> registry_;
+
   scoped_refptr<base::RefCountedData<bool>> destroyed_;
 
   base::ThreadChecker thread_checker_;