Minor cleanup preparing for recording parent-child data

Minor cleanup preparing for recording parent-child data

I removed the branch-free macro.  I really need to 
use a profiler to see if such changes are valuable.

I cleaned up the placement of slots, putting the
rare-to-use values together (so they'll probably get
better handled by cache lines.

r=rtenneti
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113749

[ramant (doing other things), 2011-12-08 19:46:16]

lgtm