Compositor-backed canvas contexts keep their transports tied to a single
Compositor connection. When that connection dies, the 2D backing
storage and WebGL GL objects disappear with it, but WebContent does not
surface the loss to canvas contexts or create fresh host contexts after
reconnect.
Track compositor loss through the WebContent connection, mark WebGL
contexts lost, dispatch the standard context events, and rebuild the
remote proxy when the page opts into restoration. For 2D canvas, queue
the canvas context loss steps, discard the dead backing storage, and
create new storage before firing contextrestored.
Canvas rendering is a major remaining path where WebContent directly
owns GPU-facing drawing state. Back 2D and WebGL canvas contexts with
remote Compositor transports, so WebContent talks to canvas surfaces
through IPC while the Compositor owns the rasterization resources.
This is a large step toward GPU sandboxing because canvas GPU work now
lives behind the Compositor boundary. It also gives OffscreenCanvas the
process-independent canvas plumbing that HTMLCanvasElement now uses,
making worker-owned canvases possible without another WebContent-local
rendering path.
Previously, the LibWeb bindings generator would output multiple per
interface files like Prototype/Constructor/Namespace/GlobalMixin
depending on the contents of that IDL file.
This complicates the build system as it means that it does not know
what files will be generated without knowledge of the contents of that
IDL file.
Instead, for each IDL file only generate a single Bindings/<IDLFile>.h
and Bindings/<IDLFile>.cpp.
Before this change, we were going through the chain of base classes for
each IDL interface object and having them set the prototype to their
prototype.
Instead of doing that, reorder things so that we set the right prototype
immediately in Foo::initialize(), and then don't bother in all the base
class overrides.
This knocks off a ~1% profile item on Speedometer 3.
This way we could be sure that context object won't be deallocated
before any of the objects that belong to it.
Having a context pointer is also going to be used in upcoming changes
to generate an INVALID_OPERATION error if an object does not belong to
the context it's being used in.
