Bug 1696842 - Establish raster roots for more picture composite modes r=gfx-reviewers,lsalzman
Bug 1696842 - Establish raster roots for more picture composite modes r=gfx-reviewers,lsalzman

Add MixBlend and ComponentTransfer to the picture composite modes that
unconditionally establish a raster root.

All the known bugs with the raster root code have been fixed, so let's
start incrementally enabling raster roots for more picture modes, and
fix any regressions that come from these before making raster roots
the default for all surfaces.

Differential Revision: https://phabricator.services.mozilla.com/D117954

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/28c7b58df8e4d6f8cd4914b197031db988dc76ea

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender