Fix incremental marking of native context when bootstrapping.

Fix incremental marking of native context when bootstrapping.

This should fix one of the arm64 build breaks - we have tried to mark
half-initialized native context there, but the normalized_map_cache
entry was still undefined.

R=hpayer@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=21283

[Hannes Payer (out of office), 2014-05-13 08:45:59]

lgtm

[Jarin, 2014-05-13 08:48:46]

Committed patchset #2 manually as r21283 (presubmit successful).