FastElementsAccessor::SetLengthWithoutNormalize() handlified.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/208313012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20214 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Replaced unreachable code in DoStoreNamedField by an assertion.

Port r20194 (2dfda0f)

Original commit message:
This is part of the effort to assign an environment if and only if we can deopt.

Removed some related dead code on the way.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/210023004

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20215 ce2b1a6d-e550-0410-aec6-3dcde31c8c00