This is a monster patch that turns all EventTargets into GC-allocated
PlatformObjects. Their C++ wrapper classes are removed, and the LibJS
garbage collector is now responsible for their lifetimes.
There's a fair amount of hacks and band-aids in this patch, and we'll
have a lot of cleanup to do after this.
Specifically HTMLIFrameElement and HTMLObjectElement. HTMLEmbedElement
will gain it automatically once it's also converted to inherit from
BrowsingContextContainer.
We will soon have two DOM nodes which contain nested browsing contexts:
HTMLIFrameElement and HTMLObjectElement. Only HTMLIFrameElement should
have its nested context created automatically upon insertion, so move
the invocation of that logic to HTMLIFrameElement.
Once we paint, it's way too late for this check to happen anyway.
Additionally, the spec's steps for retrieving the content document
assume that both the browsing context's active document and the
container's node document are non-null, which evidently isn't always the
case here, as seen by crashes on the SerenityOS 2nd and 3rd birthday
pages (I'm not sure about the details though).
Fixes#12565.
The "completely finish loading" algorithm (from the HTML spec) is
responsible for sending a "load" event to nested browsing context
containers (iframes).
This patch removes the old mechanism for sending "load" events, which we
had mistakenly kept around, causing two events to be sent instead of
one. :^)
This changes allows for nested browser contexts to be embedded in the
serialized JSON of their container element (like `iframe`) and enables
their inspection in the DOM Inspector.
