There were two problems:
1) We didn't update the demo's use of RenderImage when we switched RenderImage
to take a sky.Image rather than a URL.
2) Scheduling a layout no longer ensured a visual update, which meant we'd
never actually flushLayout unless something else ensured a visual update.
TBR=jackson@google.com
Review URL: https://codereview.chromium.org/1221273002.