Unreviewed build fix for the GTK+ port after r169987.

* UIProcess/API/gtk/WebKitWebView.cpp:
(webkit_web_view_can_execute_editing_command): The first passed-in parameter
is now a reference to a const String object.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169988 268f45cc-cd09-0410-ab3c-d52691b4dbfc