I'd worry about those problems (e.g. "revert wars") if and when you ever see them happen. They will be easy enough to spot.

MSFT is already contributing to Chrome, e.g. https://bugs.chromium.org/p/chromium/issues/detail?id=893460

From my position sitting at the crossroads of Clang/LLVM and Chrome (the team I work on developed clang-cl), all the interactions I've seen with MSFT are positive.