One of my previous commits removed this, so I am now restoring it.

This commit also contains a bit of cleanup from previous commits by
removing some unneeded types.

It also fixes traceur by porting ag/2409144 to master.

Bug: 62413700, 62547086
Test: Built, flashed, and booted Marlin.  Verified that the files have
the correct context.  Verified that atrace and traceur work.

Change-Id: I76fa0e9060aff554687d57ab3976c8704a4068f0