Fix rebaseline-o-matic logging

Fix rebaseline-o-matic logging

readline blocks, so reading stdout, then stderr doesn't make any
sense because we'll block on each on. So if we print only to one
of them, we'll just wait until the process completes.

Also, simplify the readline loop in RebaselineOMatic to just
use readline instead of poll. That way it avoids missing any
output between the last poll and when the process finishes.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176146

[ojan, 2014-06-14 00:28:26]

This is kind of hard to test. :(

[Dirk Pranke, 2014-06-14 00:32:38]

lgtm

[ojan, 2014-06-14 00:33:00]

The CQ bit was checked by ojan@chromium.org

[commit-bot: I haz the power, 2014-06-14 00:33:33]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ojan@chromium.org/329873005/60001

[commit-bot: I haz the power, 2014-06-14 01:36:54]

Change committed as 176146