X87: Encapsulate megamorphic load/tail-call in hydrogen

X87: Encapsulate megamorphic load/tail-call in hydrogen

port r23772.

original commit message:

  To aid vector-based load ic work, we need to be able to handle
  the megamorphic load case in hydrogen. A simple approach is to
  wrap the probe activity in a hydrogen instruction.

  The instruction is novel in that it always tail-calls away.

BUG=

[Jing, 2014-09-11 07:01:02]

jing.bao@intel.com changed reviewers:
+ mvstanton@chromium.org, weiliang.lin@intel.com

[Weiliang, 2014-09-12 01:39:03]

lgtm

[Weiliang, 2014-09-12 01:42:54]

Committed as r23889