Post process trace protos to filter out disallowed fields from trace

Would remove all fields that are not allowed from the trace.
Would also reduce the space used by length fields to exactly the
bytes required instead of max length bytes.

Change-Id: I03248877377d29084e88cd7e0abde33dde80c07d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2644677


Commit-Queue: ssid <ssid@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#848171}