MIPS: port Remove the fcontext field from all contexts.

MIPS: port Remove the fcontext field from all contexts.

Ported 8452 (8a2a360)

Original commit message:
Before: every context cached the nearest enclosing function context. This
assumed that for nested contexts (i.e., with and catch contexts) the
enclosing function had a materialized link in the context chain.
Now: when necessary, we loop up the context chain to find such a context.
This enables catch contexts without forcing the enclosing function to
allocate its own context.

BUG=
TEST=

Committed: http://code.google.com/p/v8/source/detail?r=8477

[Kevin Millikin (Chromium), 2011-06-30 08:21:01]

LGTM, I'll commit it.

http://codereview.chromium.org/7284025/diff/1/src/mips/macro-assembler-mips.cc
File src/mips/macro-assembler-mips.cc (left):

http://codereview.chromium.org/7284025/diff/1/src/mips/macro-assembler-mips.c...
src/mips/macro-assembler-mips.cc:3723: if (emit_debug_code()) {
BTW, this debug check was removed from ARM because I couldn't think of a simple
way to do it with only one scratch register---and didn't want to pass in a
scratch register just for debug code.

It's still on IA32 and x64, so maybe you can think of a good way to introduce it
here?