fix [2170319] gmail bulk operation checkbox latency on passion

This also fixes [2152536] ANR in browser

When SF is enqueuing buffers faster than SF dequeues them.
The update flag in SF is not counted and under some situations SF will only
dequeue the first buffer. The state at this point is not technically
corrupted, it's valid, but just delayed by one buffer.

In the case of the Browser ANR, because the last enqueued buffer was delayed
the resizing of the current buffer couldn't happen.

The system would always fall back onto its feet if anything -else- in
tried to draw, because the "late" buffer would be picked up then.