Add a scenario name to memlog slow-reports

The slow-reports are setting a scenario name into the trace metadata.
This is allowing to know from which trigger the trace is coming from.

This CL is adding the code to add the "MEMLOG" scenario name for the
memlog related slow-reports.

R=erikchen

Change-Id: I561a63649e2990d89652502e2b9c021376850c7a
Reviewed-on: https://chromium-review.googlesource.com/1144261
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576897}
1 file changed