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The argument filter is required to make sure only whitelisted arguments
are present in traces from users. To be able to use Perfetto backend in
slow reports in JSON mode, this CL implements argument filtering as it
exists in TraceLog. The metadata filtering is done by
TracingControllerImpl with both backends.

BUG=925148

Change-Id: I65ad53a8ccfea8f721b7fbf4dd7e66969e50fda2
Reviewed-on: https://chromium-review.googlesource.com/c/1464433
Commit-Queue: ssid <ssid@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632001}