Special case the recording of constant pool entries in the slot buffer.

This CL enables RelocInfo pointers which live in the constant pool to be treated
as normal pointers by the slot buffer, avoiding the requirement of creating fake
RelocInfo objects during UpdateSlots() in order to update these slots.  This
is possible because constant pool entries are just pointers and don't require
the RelocInfo machinary to be updated.

EmbeddedObject constant pool entries can be added untyped to the slot buffer,
while code targets are still typed in order to correctly update the target
address based on the relocated code object.

Note: this is required in order to enable OOL constant pool support on Arm, but
should be benifitial for the current inline constant pool used by Arm code.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/179813005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19772 ce2b1a6d-e550-0410-aec6-3dcde31c8c00