inspector: add virtual destructor to WorkerDelegate

Currently the WorkerDelegate class has a virtual function
but no virtual destructor which means that if delete is called on a
WorkerDelegate pointer to a derived instance, the derived destructor
will not get called.

The following warning is currently being printed when
compiling:

warning: delete called on 'node::inspector::WorkerDelegate' that is
abstract but has non-virtual destructor [-Wdelete-non-virtual-dtor]
    delete __ptr;
    ^

This commit adds a virtual destructor.

PR-URL: #23215
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: danbev

src/inspector/worker_inspector.h

@@ -21,6 +21,7 @@ class WorkerDelegate {
                              const std::string& url,
                              bool waiting,
                              std::shared_ptr<MainThreadHandle> worker) = 0;
+  virtual ~WorkerDelegate() {}
 };
 
 class WorkerManagerEventHandle {