I hadn't built Emacs lately with xwidgets support. When I tried it on Fedora 29 
via './configure --with-xwidgets --enable-gcc-warnings' the build failed with 
the diagnostics at the end of this message. Apparently WebKitGTK has mutated and 
Emacs hasn't kept up. Although I plan to work around the immediate problem by 
installing the attached patch on master, could an xwidgets expert please fix 
this the "right" way by using the JavaScriptCore GLib API instead? Thanks.

   CC       xwidget.o
xwidget.c: In function ‘webkit_javascript_finished_cb’:
xwidget.c:393:2: error: ‘webkit_javascript_result_get_global_context’ is 
deprecated [-Werror=deprecated-declarations]
   context = webkit_javascript_result_get_global_context (js_result);
   ^~~~~~~
In file included from /usr/include/webkitgtk-4.0/webkit2/webkit2.h:54,
                  from xwidget.c:30:
/usr/include/webkitgtk-4.0/webkit2/WebKitJavascriptResult.h:49:1: note: declared 
here
  webkit_javascript_result_get_global_context (WebKitJavascriptResult *js_result);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xwidget.c:394:2: error: ‘webkit_javascript_result_get_value’ is deprecated: Use 
'webkit_javascript_result_get_js_value' instead [-Werror=deprecated-declarations]
   value = webkit_javascript_result_get_value (js_result);
   ^~~~~
In file included from /usr/include/webkitgtk-4.0/webkit2/webkit2.h:54,
                  from xwidget.c:30:
/usr/include/webkitgtk-4.0/webkit2/WebKitJavascriptResult.h:52:1: note: declared 
here
  webkit_javascript_result_get_value          (WebKitJavascriptResult *js_result);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[1]: *** [Makefile:384: xwidget.o] Error 1
make[1]: Leaving directory '/home/eggert/src/gnu/emacs/master-tmp/src'
make: *** [Makefile:421: src] Error 2