[Variations] Enable Safe Mode in monitoring mode.

Prior to launching Safe Mode, we want to verify that there won't be a
significant number of false positives, which might otherwise cause more harm
than good. This CL adds metrics to measure how often Safe Mode would trigger,
without actually enabling safe mode even when the heuristics say it should
trigger.

[email protected]

Bug: 727984
Change-Id: I83b909bf81ec8c6416f47151c17fe4e53725ee3c
Reviewed-on: https://chromium-review.googlesource.com/570731
Commit-Queue: Ilya Sherman <[email protected]>
Reviewed-by: Alexei Svitkine (slow) <[email protected]>
Cr-Commit-Position: refs/heads/master@{#486966}
7 files changed