Hi,

There are some problems with an input form and a textarea as
follows:

・Can't enter text at the beginnig of input/textarea if there is
  a link just above the form.
・Can't enter space at (1- eol).
・Can't kill a line.
・Can't undo.
・Can't retrieve the response for the submit in a certain site.
・Padding width gets incorrect if there is a wide character.
・A major mode command like `g' doesn't work at the right outside
  of textarea.

I tested and tried to improve them in mainly:
<https://www.excite.co.jp/world/english/>    [1]
A patch is below.  Some of them would have to be improved further,
though.

Thanks.

[1] This is an English-Japanese translation service; you can
find the textarea slot for entering an original English text at
the line 191 in an eww buffer.  Please note that the translation
is not so accurate. ;-)

P.S. I will be absent from the net till Thursday, sorry.

In GNU Emacs 26.0.90 (build 1, i686-pc-cygwin, GTK+ Version 3.18.9)
 of 2017-10-20 built on localhost
Windowing system distributor 'The Cygwin/X Project', version 11.0.11900000

* lisp/net/eww.el (eww, eww-reload): Disable undo.
(eww-render): Enable undo when a user enters things in input/textarea.
(eww-tag-a): Make keymap prop non-sticky.
(eww-kill-line): New command.
(eww-textarea-map): Use it.
(eww-process-text-input): Enable a user to enter space at (1- eol);
don't break the form when killing a line at the beginning of the form.
(eww-tag-textarea): Treat textarea's text as its value if it is null;
work the padding correctly when there is a wide character;
make keymap prop non-sticky.