Hi!

While I am trying out xwidget in master branch, I found many xwidget
views are made and kept in `xwidget-view-list' for one xwidget model
while I have only one xwidget buffer open.

I am attaching a patch for the problem and here is how to test.

Test procedure:

1. `xwidget-webkit-browse-url' to a web page

2. Resize emacs frame, scroll it up/down several times

3. C-x b to *scratch* and C-x 1

4. check with `(length xwidget-view-list)'

Expected output is 1
Actual output is > 1

Thanks,