MIPS: Refactoring of code generation for declarations, in preparation for modules.

MIPS: Refactoring of code generation for declarations, in preparation for modules.

Port r11331 (bd7843a0)

Original commit message:
Refactoring of code generation for declarations, in preparation for modules.

Do proper dispatch on declaration type instead of mingling together
different code generation paths. Once we add more declaration forms,
this is more scalable.

In separate steps, I'd like to (1) clean up the logic for DeclareGlobal,
and (2) try to reduce the special handling of the name function var if
possible.

BUG=
TEST=

[palfia, 2012-04-16 22:06:53]

Building and testing on mips also requires the following patches to be landed:
http://codereview.chromium.org/10106007/
http://codereview.chromium.org/10103008/

[rossberg, 2012-04-18 14:37:42]

lgtm

[rossberg, 2012-04-18 15:44:32]

Landed as r11372.