[Sync] Remove backend unrecoverable error handler

sync/util/test_unrecoverable_error_handler.h

Index: sync/util/test_unrecoverable_error_handler.h
diff --git a/sync/util/test_unrecoverable_error_handler.h b/sync/util/test_unrecoverable_error_handler.h
index ae0610c576b2af7ed029f088a3775358b902782a..1546783c834010befd7d0b11ff464922e398face 100644
--- a/sync/util/test_unrecoverable_error_handler.h
+++ b/sync/util/test_unrecoverable_error_handler.h
@@ -6,6 +6,7 @@
 #define SYNC_INTERNAL_API_INCLUDES_TEST_UNRECOVERABLE_ERROR_HANDLER_H_
 
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "sync/internal_api/public/util/unrecoverable_error_handler.h"
 
 namespace syncer {
@@ -19,6 +20,11 @@ class TestUnrecoverableErrorHandler : public UnrecoverableErrorHandler {
 
   void OnUnrecoverableError(const tracked_objects::Location& from_here,
                             const std::string& message) override;
+
+  base::WeakPtr<TestUnrecoverableErrorHandler> GetWeakPtr();
+
+ private:
+  base::WeakPtrFactory<TestUnrecoverableErrorHandler> weak_ptr_factory_;
 };
 
 }  // namespace syncer