These benchmarks are intended to compare the overhead of async-await vs.
a naive promise implementation vs. the babel async-await transformation.
The functions in the benchmark don't do any work themselves, so results
should reflect only overhead of the chosen implementation.

Current numbers on my local machine (higher is better):

BaselineES2017-AsyncAwait(Score): 2006
BaselineNaivePromises-AsyncAwait(Score): 7470
Native-AsyncAwait(Score): 3640

BUG=v8:5639

Review-Url: https://codereview.chromium.org/2577393002
Cr-Commit-Position: refs/heads/master@{#41860}