WebKit Igalia Periodical #69

Made RenderLayer creation conditional for SVG renderers in the new Layer-Based SVG Engine (LBSE), so a layer is now only created when one is actually needed for intrinsic reasons (3D transforms, opacity, etc.) instead of unconditionally for every renderer. Plain 2D transforms no longer force a layer and are applied directly during painting. This is the groundwork for follow-up patches that remove the intrinsic need for layers when applying clipping, masking and filters to SVG subtrees. It is an important milestone towards reducing the overhead that has been holding back LBSE performance compared to the legacy SVG engine.

Fixed the paint order of non-composited children around composited SVG siblings in the Layer-Based SVG Engine (LBSE). A layered container paints its children from a single flat list in DOM (and SVG paint) order, but some children are composited into their own GraphicsLayer for reasons like will-change, a 3D transform or certain opacity cases. The flat child list is now split into contiguous paint-order segments at those boundaries, with each run of plain children painted by its own overlay layer placed at the correct depth in the compositor's child list. This keeps every child in its DOM order without giving trailing siblings a RenderLayer or backing store of their own, and a container with no composited children produces no segments at all, so the common case costs nothing. This allows us to support composition within LBSE subtrees in a performant way, after dropping the requirement that every renderer creates a layer.

Fixed initial decoding issues on LibWebRTC on platforms that do video decoding on the final playback stage (for efficiency and performance), instead of on the LibWebRTC decoder component.

Added support for producing WebP images with canvas' .toDataURL(). Using 1.0 as the quality setting will produce lossless images, which matches the behaviour of Chromium and Firefox.