Replace generic KeyedStore stub with megamorphic version

Replace generic KeyedStore stub with megamorphic version

This is a follow-up to https://codereview.chromium.org/859943003.

Committed: https://crrev.com/62f761903a5294ec91687d5a108544914015899a
Cr-Commit-Position: refs/heads/master@{#26161}

[Jakob Kummerow, 2015-01-20 13:10:53]

jkummerow@chromium.org changed reviewers:
+ verwaest@chromium.org

[Jakob Kummerow, 2015-01-20 13:10:54]

PTAL.

I've left some occurrences of the string "generic", e.g. in the macro name
TRACE_GENERIC_IC, because I didn't think clarity would be improved by changing
those to "megamorphic" (as they describe the high-level concept of using a very
generic handler, rather than The One Generic Stub), but I'm happy to rename
things if you'd like.

[Toon Verwaest, 2015-01-20 13:15:55]

lgtm

[Jakob Kummerow, 2015-01-20 13:26:23]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-01-20 13:26:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/847963004/1

[commit-bot: I haz the power, 2015-01-20 14:16:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-20 14:16:19]

Patchset 1 (id:??) landed as
https://crrev.com/62f761903a5294ec91687d5a108544914015899a
Cr-Commit-Position: refs/heads/master@{#26161}