The concept of a "resource header" is not well specced, since it is
unclear what a "resource" is. That said, it most closely matches a
"response" as part of the navigation params.
With this change, we now delay loading the document until either two
things happen:
1. We reached the end of the file
2. We processed 1445 bytes (as defined by spec)
We initially store bytes in the resource header and then after loading
parse the stored bytes. Any subsequent loading will process as before.
Part of #14024
Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>
a672ffb850