Add support to the yaml reader and writer to be able to specify
that a primitive should set the PREFER_COMPOSITOR_SURFACE flag.

This flag is not currently used, but in future will signal the
picture caching code to promote a primitive to draw on a native
compositor surface where possible.

Differential Revision: https://phabricator.services.mozilla.com/D62693

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/1e1ffcbadfb2350ecda25b8752b3c07c2f2d0722

…=nical,Bert

Simplify some of the logic related to handling multiple
compositor surfaces in future, specifically:

* Only rebuild the tiles map when the tile rect changes.
* Remove need for tiles_to_draw array.

Differential Revision: https://phabricator.services.mozilla.com/D62694

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/0c0eb80974b03f6cc153616fe21c8dc229b25c3e

…hs in local space. r=lsalzman

This patch makes the CPU side incorporate the raster scale when
calculating the subpixel position of a glyph. It also makes the shader
side not include the glyph scale factor when recalculating the glyph
position (since it was not known/used when determining the subpixel
position in the first place). This makes the subpixel position stable
when we transition between Screen and Local(raster_scale) spaces.

Differential Revision: https://phabricator.services.mozilla.com/D62812

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/9bd4120bc9779fe1c42fb45246044a23f2e95d25

Differential Revision: https://phabricator.services.mozilla.com/D62851

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/fc74126fedeb2bb945db4d52e54266c955e9bbe7