Use a per-isolate cache for the date object JS bits

Use a per-isolate cache for the date object JS bits

The old per-context cache made it difficult for the embedder to notify
v8 of date/time configuration changes. The embedder had to enter all
contexts for the isolate and notify v8 for each context.

With the new per-isolate cache, the embedder only needs to notify v8
once per isolate.

BUG=348856
LOG=y
R=dcarney@chromium.org, ulan@chromium.org
TEST=cctest/test-date

Committed: https://code.google.com/p/v8/source/detail?r=19784

[dcarney, 2014-03-11 07:37:31]

lgtm

[dcarney, 2014-03-11 08:17:18]

lgtm, again

[jochen (gone - plz use gerrit), 2014-03-11 09:04:23]

Committed patchset #2 manually as r19784 (presubmit successful).