remove log.getChunks

The only consumer of this method, aside from `log.readlines` and `log.getText`, was `SetPropertyFromCommand`.  This contains the equivalent of #1030 (Add a BufferLogObserver and use it in SetPropertyFromCommand) for nine, and then removes `getChunks`.

1365695 and e7a829e are the commits to review here -- the "Files Changed" view won't be very helpful:
* bf65927 and 2429b31 are from #1028.
* 75355ee, 1ec1dd5, and 689565e are from #1029.