The display list is an immutable data structure, so once it's created,
rasterization can be moved to a separate thread. This allows more room
for performing other tasks between processing HTML rendering tasks.
This change makes PaintingSurface, ImmutableBitmap, and GlyphRun atomic
ref-counted, as they are shared between the main and rendering threads
by being included in the display list.
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
Fix the function signatures of Canvas.toDataURL() and Canvas.toBlob()
and make both functions accept non-numbers as the quality parameter, in
which case it will just use the default quality instead of raising an
exception.
This makes toDataURL.arguments.1.html, toDataURL.arguments.2.html and
toDataURL.jpeg.quality.notnumber.html in
wpt/html/semantics/embedded-content/the-canvas-element pass :^)
