VectorICs: Bugfix in KeyedStore dispatcher.

VectorICs: Bugfix in KeyedStore dispatcher.

The dispatcher failed to MISS properly when configured as a monomorphic
keyed string store, causing a crash.

BUG=v8:4495
LOG=N
R=jkummerow@chromium.org

Committed: https://crrev.com/2f2302f08bce6fc98b2f1c89b6014a5f78a784c5
Cr-Commit-Position: refs/heads/master@{#31362}

[mvstanton, 2015-10-19 08:23:57]

Hi Jakob,
I'm using "bool is_polymorphic" to separate the case where I know the feedback
array has >= 4 items from the case where it may be monomorphic, when the array
may be smaller. This fix mirrors logic done for the keyed load ic before, see
method HandleArrayCases line 4432.

Thanks for the look. The arm, mips and x64 platforms are unaffected.

[Jakob Kummerow, 2015-10-19 08:56:11]

lgtm

[mvstanton, 2015-10-19 09:17:56]

The CQ bit was checked by mvstanton@chromium.org

[mvstanton, 2015-10-19 09:17:56]

The patchset sent to the CQ was uploaded after l-g-t-m from
jkummerow@chromium.org
Link to the patchset: https://codereview.chromium.org/1415533003/#ps20001
(title: "Adding x87 port.")

[commit-bot: I haz the power, 2015-10-19 09:18:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1415533003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1415533003/20001

[commit-bot: I haz the power, 2015-10-19 09:51:29]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-19 09:51:53]

Patchset 2 (id:??) landed as
https://crrev.com/2f2302f08bce6fc98b2f1c89b6014a5f78a784c5
Cr-Commit-Position: refs/heads/master@{#31362}