deps: backport ff7d70b from V8's upstream
Original commit message:
Update BitField3 type in gen-postmortem-metadata.py
Since https://codereview.chromium.org/272163002, BitField3 is a raw uint32 field, and not a SMI anymore.
Update tools/gen-postmortem-metadata.py so that post-mortem tools can work with versions of V8 that shipped after that change.
This change was merged in github.com/joyent/node right before node v0.12.0 was released.
TEST=mdb_v8, a post-mortem debugging tool running on SmartOS, has been using this change since Node.js v0.12.0 was released
BUG=
Review URL: https://codereview.chromium.org/1296743003
Cr-Commit-Position: refs/heads/master@{#30839}
This is necessary to allow mdb_v8 to work properly with node v4.x, so this would need to be backported to the v4.x branch.
/cc @nodejs/post-mortem