MIPS: Skip canonicalization check in LStoreKeyedFastDoubleElement when it is not needed

MIPS: Skip canonicalization check in LStoreKeyedFastDoubleElement when it is not needed

Port r11278 (e5dc7ebd).

Original commit message:

Skip canonicalization check in LStoreKeyedFastDoubleElement when it is not needed:

- if value is a result of integer32 to double conversion (can't be NaN);

- if value was loaded from fast double backing store (already canonicalized).

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=11366

[kalmard, 2012-04-17 14:45:03]

rebased on r11356

[Vyacheslav Egorov (Chromium), 2012-04-18 10:42:03]

LGTM, landing