bug#36633: Scrolling by pixels: visible stretch glyphs overwrite header-line.

[Keith David Bershatsky]

Thank you, Alan, for your work on issue 36633.

Today, I built an Emacs master branch on OSX 10.6.8 using:

Last Commit : Tue Jul 16 16:04:54 2019 -0700
            : Glenn Morris <rgm@gnu.org>
            : 7e70c78867ab2b8e280f6a087b32a947b13776a7
            : An electric test is now passing

with the following configuration:

CFLAGS='-Wall -O0 -g3' ./configure \
--with-ns \
--enable-checking='yes,glyphs' \
--enable-check-lisp-object-type \
--without-compress-install \
--with-gnutls=no \
--with-mailutils \
--without-makeinfo

I did not see any visible change using the test outlined in the original post.  
Here is a new screen-recording using the above-mentioned build:

https://youtu.be/IS3Dgy-326U