MIPS: Mark null and undefined as undetectable, and use it to handle abstract equality comparison in…

MIPS: Mark null and undefined as undetectable, and use it to handle abstract equality comparison in the generic compare ic.

Port for https://codereview.chromium.org/1683643002/

Original commit message:
Marking as undetectable makes abstract equality of null, undefined, and
other undetectable objects easier. Supporting it in the generic compare
IC significantly speeds up dynamic comparison between those values and
JSReceivers by not falling back to the runtime.

BUG=

[balazs.kilvady, 2016-02-09 19:55:55]

Description was changed from

==========
MIPS: Mark null and undefined as undetectable, and use it to handle abstract
equality comparison in the generic compare ic.

Port for https://codereview.chromium.org/1683643002/

Original commit message:
Marking as undetectable makes abstract equality of null, undefined, and
other undetectable objects easier. Supporting it in the generic compare
IC significantly speeds up dynamic comparison between those values and
JSReceivers by not falling back to the runtime.

BUG=
==========

to

==========
MIPS: Mark null and undefined as undetectable, and use it to handle abstract
equality comparison in the generic compare ic.

Port for https://codereview.chromium.org/1683643002/

Original commit message:
Marking as undetectable makes abstract equality of null, undefined, and
other undetectable objects easier. Supporting it in the generic compare
IC significantly speeds up dynamic comparison between those values and
JSReceivers by not falling back to the runtime.

BUG=
==========

[balazs.kilvady, 2016-02-09 19:55:55]

balazs.kilvady@imgtec.com changed reviewers:
+ akos.palfi@mattakis.com, gergely.kis@imgtec.com,
ivica.bogosavljevic@imgtec.com, verwaest@chromium.org