MIPS: Generators return boxed values

MIPS: Generators return boxed values

Port r14563 (6d01adb8)

Original commit message:
Generators now box their return values in object literals of the form

  { value: VAL, done: DONE }

where DONE is false for yield expressions, and true for return
statements.

BUG=

Committed: https://code.google.com/p/v8/source/detail?r=14582

[Paul Lind, 2013-05-07 23:09:23]

lgtm

[palfia, 2013-05-07 23:14:44]

Committed manually as r14582 (presubmit successful).