I don't know about Firefox & Safari, but I think you're missing an important caveat here for Chrome:
> In directories where most contributors have already adopted clang-format, and code is already consistent with what clang-format would produce, some teams intend to experiment with standardizing on clang-format. When these local standards apply, it will be enforced by a PRESUBMIT.py check.
From the looks of it it's a lot of the tree [1].
Where manual formatting gives you some freedom in meeting the style guide, it also brings along with it errors (style guides are massive and it's not possible to remember everything) & sometimes you just make a typo. This also means that your reviewers are spending time validating against the style guide which is not only the most wasteful use of their time, it's still an imperfect process because reviewers are just like the author - they don't have the entire style guide in their head at all times and they may miss violations.
> In directories where most contributors have already adopted clang-format, and code is already consistent with what clang-format would produce, some teams intend to experiment with standardizing on clang-format. When these local standards apply, it will be enforced by a PRESUBMIT.py check.
From the looks of it it's a lot of the tree [1].
Where manual formatting gives you some freedom in meeting the style guide, it also brings along with it errors (style guides are massive and it's not possible to remember everything) & sometimes you just make a typo. This also means that your reviewers are spending time validating against the style guide which is not only the most wasteful use of their time, it's still an imperfect process because reviewers are just like the author - they don't have the entire style guide in their head at all times and they may miss violations.
[1] https://github.com/search?q=CheckPatchFormatted+repo%3Achrom...