Turns out when Windows is running in QEMU and a window scroll happens,
there are lots of little hextile rects sent. This is slow in noVNC.
- Some recording/playback improvement.
- Add test harness to drive playback of recordings.
- By pulling off the rect header in one chunk we get a 3X speedup in
Chrome and a 20% speedup in firefox (specifically for the scroll
test).
- Also, get rid of some noise from creating timers for handle_message.
Check to make sure there isn't already a pending timer first.
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