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New type of trace event macros use proto fields, for uploading
background traces

TBR=ssid@google.com

Change-Id: I91e4d211ec46bd68eee3c238d8efccbd0f342329
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2454976Reviewed-by: ssid <ssid@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815802}