Split the virtual frame into heavy and light versions.

Split the virtual frame into heavy and light versions.
The heavy version is for x86 and x64.  The light version
is for ARM and MIPS.  Remove the elements_ array from the
virtual frame in the light version.  More simplifications
to come, followed by light register allocation.
Review URL: http://codereview.chromium.org/1164002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4272 ce2b1a6d-e550-0410-aec6-3dcde31c8c00