Initialize Date parse cache with SMI instead of double to workaround sharing mutable heap numbers i…

Initialize Date parse cache with SMI instead of double to workaround sharing mutable heap numbers in snapshot.

This is the only field in the snapshot that was tracked as double.

R=verwaest@chromium.org
TEST=mjsunit/regress/regress-280531.js
BUG=280531
LOG=Y

Committed: https://code.google.com/p/v8/source/detail?r=18298

[ulan, 2013-12-11 12:47:51]

Please take a look. This is the workaround we discussed. It is small and should
be safe to merge back.

I will follow up with a fix to disable double field tracking during snapshot
generation.

[Toon Verwaest, 2013-12-11 13:06:58]

lgtm

[ulan, 2013-12-11 13:11:52]

Committed patchset #1 manually as r18298.