I have a bug where emacs can no longer paste into gmail
compose windows that are set to plain text, and the fix for
this bug 03b780e387e54c23ac9322e329aca6e5ab4f18e6
bisected as the bad commit. Reverting the commit resolves
the issue.

The issue is on linux under X11 on master at all points after
03b780. To reproduce, copy some text from emacs and try
to paste it into a gmail compose window that is set to plain
text mode.

I do not know exactly which part of the changes induced the
behavior, but reverting the commit clearly fixes the issue and
allows me to paste into plain text mode compose again.