Content offset is now stored in unscaled pixels, so that it can be
applied to tile positions during compositor rendering without unscaling
it. This means that when using it in calculations of layer size (stored
in device pixels), we need to scale it. Scene scale is now stored as a
scale rather than a transformation.
Fixes#3269.
Fixes#3042.
Instead of producing image output as soon as the first pipeline is
ready, we wait to produce the output until all pipelines are in the
idle RenderState. This should remove a race condition when running
reference tests.
Instead of waiting to create the root layer, create them as soon as the
Compositor receives the frame tree. This allows the compositor to
create a layer tree skeleton of which to hang the base layers when they
are ready.
