Default to creating new related sessions

* doc/lispref/display.texi:
* etc/NEWS: Document changes.

* lisp/xwidget.el (xwidget-insert): Accept an extra RELATED argument.
(xwidget-webkit-new-session): Pass current session as RELATED if
present.

* src/xwidget.c (Fmake_xwidget): Make RELATED argument public.

doc/lispref/display.texi

@@ -6801,8 +6801,9 @@ The WebKit component.
 
 The @var{width} and @var{height} arguments specify the widget size in
 pixels, and @var{title}, a string, specifies its title.  @var{related}
-is used internally by the WebKit widget, and is not of interest to the
-programmer.
+is used internally by the WebKit widget, and specifies another WebKit
+widget that the newly created widget should share settings and
+subprocesses with.
 @end defun
 
 @defun xwidgetp object

etc/NEWS

@@ -744,6 +744,12 @@ an exact match, then the lowercased '[menu-bar foo\ bar]' and finally
 '[menu-bar foo-bar]'.  This further improves backwards-compatibility
 when converting menus to use 'easy-menu-define'.
 
++++
+** The function `make-xwidget' now accepts an optional RELATED argument.
+This argument is used as another widget for the newly created WebKit
+widget to share settings and subprocesses with.  It must be another
+WebKit widget.
+
 +++
 ** New function `xwidget-perform-lispy-event'.
 This function allows you to send events to xwidgets.  Usually, some

lisp/xwidget.el

@@ -35,7 +35,7 @@
 (require 'bookmark)
 
 (declare-function make-xwidget "xwidget.c"
-                  (type title width height arguments &optional buffer))
+                  (type title width height arguments &optional buffer related))
 (declare-function xwidget-buffer "xwidget.c" (xwidget))
 (declare-function set-xwidget-buffer "xwidget.c" (xwidget buffer))
 (declare-function xwidget-size-request "xwidget.c" (xwidget))
@@ -59,14 +59,14 @@
   "Displaying native widgets in Emacs buffers."
   :group 'widgets)
 
-(defun xwidget-insert (pos type title width height &optional args)
+(defun xwidget-insert (pos type title width height &optional args related)
   "Insert an xwidget at position POS.
-Supply the xwidget's TYPE, TITLE, WIDTH, and HEIGHT.
+Supply the xwidget's TYPE, TITLE, WIDTH, HEIGHT, and RELATED.
 See `make-xwidget' for the possible TYPE values.
 The usage of optional argument ARGS depends on the xwidget.
 This returns the result of `make-xwidget'."
   (goto-char pos)
-  (let ((id (make-xwidget type title width height args)))
+  (let ((id (make-xwidget type title width height args nil related)))
     (put-text-property (point) (+ 1 (point))
                        'display (list 'xwidget ':xwidget id))
     id))
@@ -685,6 +685,7 @@ For example, use this to display an anchor."
   (let*
       ((bufname (generate-new-buffer-name "*xwidget-webkit*"))
        (callback (or callback #'xwidget-webkit-callback))
+       (current-session (xwidget-webkit-current-session))
        xw)
     (setq xwidget-webkit-last-session-buffer (switch-to-buffer
                                               (get-buffer-create bufname)))
@@ -697,7 +698,8 @@ For example, use this to display an anchor."
       (setq xw (xwidget-insert
                 start 'webkit bufname
                 (xwidget-window-inside-pixel-width (selected-window))
-                (xwidget-window-inside-pixel-height (selected-window)))))
+                (xwidget-window-inside-pixel-height (selected-window))
+                nil current-session)))
     (xwidget-put xw 'callback callback)
     (xwidget-webkit-mode)
     (xwidget-webkit-goto-uri (xwidget-webkit-last-session) url)))

src/xwidget.c

@@ -110,7 +110,8 @@ TYPE is a symbol which can take one of the following values:
 
 - webkit
 
-RELATED is nil, or an xwidget.  This argument is used internally.
+RELATED is nil, or an xwidget.  When constructing a WebKit widget, it
+will share the same settings and internal subprocess as RELATED.
 Returns the newly constructed xwidget, or nil if construction
 fails.  */)
   (Lisp_Object type,