deferred code snippets are highly stylized.  They always make a call
to a stub or the runtime and then return.  This change takes advantage
of that.

Creating a deferred code object now captures a snapshot of the
registers in the virtual frame.  The registers are automatically saved
on entry to the deferred code and restored on exit.

The clients of deferred code must ensure that there is no change to
the registers in the virtual frame (eg, by allocating which can cause
spilling) or to the stack pointer.  That is currently the case.

As a separate change, I will add either code to verify this constraint
or else code to forbid any frame effect.

The deferred code itself does not use the virtual frame or register
allocator (or even the code generator).  It is raw macro assembler
code.
Review URL: http://codereview.chromium.org/118226

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2112 ce2b1a6d-e550-0410-aec6-3dcde31c8c00