Show IME back button in Pie.

Updated Pie to show the alternate back button when an IME is present like the stock navigation bar does.

Change-Id: I97b385904c183a42c6d76a9f238c4b9624668576
Picture: http://i.imgur.com/T0n9bVc.png

EDIT: Fixed whitespace and tabbing
Merge "Show IME back button in Pie." into kitkat