Avoid touching members in InterfaceImpl::ErrorHandlerImpl after calling OnConnectionError

The impl_'s OnConnectionError may end up deleting the InterfaceImpl,
so save off any member variables we wanna look at (like delete_on_error_)
in a local before firing the connection error handler.

Fixes asan-detected use after frees in view_manager_unittests.

R=davemoore@chromium.org

Review URL: https://codereview.chromium.org/724563003