A lot of the tool presence/version checks we perform in flutter doctor would be useful to perform before steps that involve invocation of those tools.

Examples from the iOS side include checking Xcode and CocoaPods presence/version and presence of the Python six module before iOS build/run.

One option would be to factor out a tool class that has the ability to check presence/version of the tool and how to run it, then use this in the build step and in doctor.