Validate perf measures with async rendering

[tbranyen]

Each transaction should have unique measures, but when running in async mode, I find that events are not aligned and render incorrectly in the Chrome profiler.

[tbranyen]

This is due to the fact that measure is mapped to mount and input rather than the transaction and that marks are sampled globally. To fix this, we will need to pass in the transaction directly to makeMeasure and scope marks to each unique transaction. That should produce completely accurate profiling.