Fix field type handling in load elimination.

Fix field type handling in load elimination.

Drive-by-fix: map_set() must return a pointer to the UniqueSet
instead of a copy.

R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=20870

[Benedikt Meurer, 2014-04-20 11:13:05]

Easy starter for the new week :-)
PTAL

[Sven Panne, 2014-04-22 07:11:02]

LGTM, although this CL is actually 2 CLs, and the bigger part is the "drive-by
fix"... ;-)

[Benedikt Meurer, 2014-04-22 07:24:14]

Committed patchset #1 manually as r20870 (presubmit successful).