This version does not recycle buffers. It is meant only as an initial solution,
and the proper buffer recycling logic has been broken out into a separate change
We push a bit up the tree during preroll to learn whether there system
composited layers below each layer. During update scene, we squash down
to paint tasks, which we execute after publishing the new scene.
When we pipelined the drawing commands we caused UpdateScene to be called
before Preroll, which isn't allowed. Now we call Preroll, UpdateScene, and
Paint separately.
The new boot sequence on Fuchsia now gives us the more accurate RGB_x888 pixel
format, which we should support. Also finish pushing pixels to the screen
before drawing new pixels.
This patch should contain all the code we need to run Flutter on
Fuchsia's software framebuffer (without text). I haven't actually tried
running the code, so I'm sure it doesn't work yet.
