5267d98772
This reverts the flutter command to use shlock when flock isn't available. It seems that the mkdir method isn't as reliable as we want. I think that this is because the trap isn't always be executed, which is why I think that shlock uses PIDs to help it be more reliable. Unfortunately, that means that we're back to not working over network shares (which is where things were before I moved to the mkdir method, so not really a regression). I did leave in the mkdir method for platforms that have neither flock nor shlock (which should be very few and far between, but still), so at least we'll do some locking there now.
Dart SDK dependency
The bin/internal/engine.version file controls which version of the Flutter engine to use.
The file contains the commit hash of a commit in the https://github.com/flutter/engine repository.
That hash must have successfully been compiled on https://build.chromium.org/p/client.flutter/ and had its artifacts (the binaries that run on Android and iOS, the compiler, etc) successfully uploaded to Google Cloud Storage.
The /bin/internal/engine.merge_method file controls how we merge a pull
request created by the engine auto-roller. If it's squash, there's only one
commit for a pull request no matter how many engine commits there are inside
that pull request. If it's rebase, the number of commits in the framework is
equal to the number of engine commits in the pull request. The latter method
makes it easier to detect regressions but costs more test resources.