This is causing build breaks for Node.js w/ V8 4.6.

Map::kInObjectPropertiesOffset was been replaced by
kInObjectPropertiesOrConstructorFunctionIndexOffset in
https://codereview.chromium.org/1276533003. This is causing the post-mortem
debug information generation to fail.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1308113007

Cr-Commit-Position: refs/heads/master@{#30536}