[CFE] Attempt at 'benchmarking' intrumenter

Ultimatley this proved not very useful (for me at this time at least).
As it might be useful in the future, though, I'll land it here.

Change-Id: I7e6c7ad878d290763d2b2c0f3c372bf7f6521ea1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/184422
Commit-Queue: Jens Johansen <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: jensjoha