This is part of the rendering spec, but we had neglected to do this
before. It causes one WPT check to fail, but other browsers get the
same result on that check, so I guess we can call that a win. :^)
These are the same code, so we may as well move them up the chain. This
becomes useful in a later commit, where it will be used to rewrite
inline-flow to inline-block for layout of shadow DOM.
With this commit, all PlaybackManager can do is autoplay a file from
start to finish, with no pausing or seeking functionality.
All audio playback functionality has been removed from HTMLMediaElement
and HTMLAudioElement in anticipation of PlaybackManager taking that
over, for both audio-only and audio/video.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
Now that we have RTTI in userspace, we can do away with all this manual
hackery and use dynamic_cast.
We keep the is<T> and downcast<T> helpers since they still provide good
readability improvements. Note that unlike dynamic_cast<T>, downcast<T>
does not fail in a recoverable way, but will assert if the object being
casted is not a T.
