This is a prepatory commit to be able to handle DOM mutations. Once a
node actor is created, the DOM node it is created for must continue to
be associated with the same actor even after DOM mutations. This change
stores an identifier on the node actor, and only creates new actors when
an actor for a node does not exist.
The pattern of:
auto tab = get_tab();
auto walker = get_walker();
if (tab && walker) {
if (auto node = walker->dom_node(node_id)) {
delegate().do_something(tab->description(), node);
}
}
Is getting a bit unergonomic and is often repeated. This patch just adds
a helper to WalkerActor to do most of this work, so now we have:
if (auto node = WalkerActor::dom_node_for(get_walker(), node_id)) {
delegate().do_something(node->tab->description(), node);
}
The DevTools client will now send requests to the node actor, rather
than just sending messages to other actors on the node's behalf.
This exposed a slight issue in the way we assign actor IDs. Node actors
are created in the walker actor constructor, which executes before the
actor ID is incremented. So we must be sure to increment the actor ID
before invoking any actor constructors. Otherwise, the walker actor and
the first node actor have the same numeric ID.
