Explicit clean up before performance test measurements (#2640) Previously we were using a workaround where odd runs were removed from measurements, and executed a `clean` build instead of the measured build.
Performance tests can now specify `cleanTasks`, similar to how they specify `tasksToRun`. These `cleanTasks` will be executed before each run (warm-up and measurement runs alike).
A new column is added to performance test tables to track this new information. It is a nullable column to allow for test results added by older versions of Gradle.
I've updated the task output caching tests and the Maven vs. Gradle comparisons to declare `cleanTasks` instead of the old hack with the odd-even runs.