[Sync] Remove backend unrecoverable error handler

sync/util/test_unrecoverable_error_handler.cc

Index: sync/util/test_unrecoverable_error_handler.cc
diff --git a/sync/util/test_unrecoverable_error_handler.cc b/sync/util/test_unrecoverable_error_handler.cc
index 4bdbf3dc732e847e981a7c104baf09b32a48490e..14d39e6bdffa5c22e4724c993db3fd10f9491d53 100644
--- a/sync/util/test_unrecoverable_error_handler.cc
+++ b/sync/util/test_unrecoverable_error_handler.cc
@@ -8,7 +8,8 @@
 
 namespace syncer {
 
-TestUnrecoverableErrorHandler::TestUnrecoverableErrorHandler() {}
+TestUnrecoverableErrorHandler::TestUnrecoverableErrorHandler()
+    : weak_ptr_factory_(this) {}
 
 TestUnrecoverableErrorHandler::~TestUnrecoverableErrorHandler() {}
 
@@ -19,5 +20,10 @@ void TestUnrecoverableErrorHandler::OnUnrecoverableError(
       << from_here.function_name() << ": " << message;
 }
 
+base::WeakPtr<TestUnrecoverableErrorHandler>
+TestUnrecoverableErrorHandler::GetWeakPtr() {
+  return weak_ptr_factory_.GetWeakPtr();
+}
+
 }  // namespace syncer