Reland MIPS: Vector-ICs - speed towards the monomorphic exit as quickly as possible.

Reland MIPS: Vector-ICs - speed towards the monomorphic exit as quickly as possible.

Port 35a67b745d862c5b1f584c2786ebf1369dc4f1ff

Original commit message:
Thanks to some careful assumptions, we can examine the object found at
vector[slot] and trust it's a heap object where the second field is
either a map if it's a WeakCell, or definitely not a map if it's a
Symbol, String or FixedArray. Use this to save a memory read.

BUG=

Review URL: https://codereview.chromium.org/1053843003

Cr-Commit-Position: refs/heads/master@{#27757}

Committed: https://crrev.com/80f24f7a4c2037c677531db21643f20e4dffc789
Cr-Commit-Position: refs/heads/master@{#27893}

[paul.l..., 2015-04-16 02:38:14]

paul.lind@imgtec.com changed reviewers:
+ akos.palfi@imgtec.com, balazs.kilvady@imgtec.com,
dusan.milosavljevic@imgtec.com, mvstanton@chromium.org

[paul.l..., 2015-04-16 02:38:15]

This should land after the fix in https://codereview.chromium.org/1074123004/

[mvstanton, 2015-04-16 06:30:09]

lgtm

[paul.l..., 2015-04-16 15:33:25]

The CQ bit was checked by paul.lind@imgtec.com

[commit-bot: I haz the power, 2015-04-16 15:33:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1083413003/1

[commit-bot: I haz the power, 2015-04-16 16:05:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 16:06:07]

Patchset 1 (id:??) landed as
https://crrev.com/80f24f7a4c2037c677531db21643f20e4dffc789
Cr-Commit-Position: refs/heads/master@{#27893}