Ion progress bar requests must always happen
on the main handler

Change-Id: I2fe0bfe979173116df667f63ad4d7777c3103ebb
Merge branch 'master' of https://github.com/koush/ion

# By Koushik Dutta
# Via Koushik Dutta
* 'master' of https://github.com/koush/ion:
  Ion progress bar requests must always happen on the main handler