X87: CallIC customization stubs must accept that a vector slot is cleared.

X87: CallIC customization stubs must accept that a vector slot is cleared.

port r22668.

original commit message:
  CallIC customization stubs must accept that a vector slot is cleared.

  The CallIC Array custom IC stub read from the type vector, expecting
  to get an AllocationSite. But there are paths in the system where a type
  vector can be re-created with default values, even though we currently
  grant an exception to clearing of vector slots with AllocationSites in
  them at gc time.

BUG=

[chunyang.dai, 2014-07-30 06:39:31]

weiliang.
please review this porting patch.

thanks.

[Weiliang, 2014-07-30 08:21:31]

lgtm

[Weiliang, 2014-07-30 08:22:30]

Committed as r22693