This is an intermediate CL to move the complete --trace-map infrastructure to
a log-based version.

Change-Id: I0673052b1b87fe338e38dc609434a52af6a0652d
Reviewed-on: https://chromium-review.googlesource.com/738835
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48988}