Currently, some benchmarks (I saw it on the flutter_gallery_ios__transition_perf) are doing a flutter build before doing a flutter drive. It seems like the build step is redundant because flutter drive will trigger another build (and since we don't have incremental builds, that one take as long as the first one).

If we eliminate the first build, we would therefore also cut down the time it takes to execute benchmarks.

/cc @yjbanov