[build] Port latest MB from Chromium

This ports the MB script from Chromium until revision:
https://crrev.com/66958462e684149bcb220000868e8247096e435b

The main difference is the removed gyp support.

This reapplies V8-side changes from:
https://crrev.com/41d9e8571419acd3547c9810c55c5516cc4dee79
https://crrev.com/1cd6fd9ff8e88bffa7cbec7131b85ff086dc128c

Bug: chromium:772804
Change-Id: I530e01df0c2343e961519ac27b1e58a01bb63743
Reviewed-on: https://chromium-review.googlesource.com/911073Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51215}