When generating display lists for WebRender, we were not caching the
draw result via nsDisplayItemGenericImageGeometry::UpdateDrawResult (or
similar) after completing CreateWebRenderCommands. This is important
because reftests use this to force sync decoding for images; it may be a
reason for image-related intermittent failures on *-qr builds.
Additionally, we may have been requesting fallback in cases where fallback
could not do anything more than WebRender could. For example, if we can't
get an image container yet, there is no point in requesting fallback
because it might just be we haven't started decoding yet. We should just
return the actual draw result in such cases.
In addition to the image container, the draw result can also be useful
for callers to know whether or not the surface(s) in the container are
fully decoded or not. This is used in subsequent parts to avoid
flickering in some cases.
Andrew Osmond
Emilio Cobos Álvarez
Samathy Barratt
Ciure Andrei