This will allow for embedders to easily implement their own Platform
without duplicating the tracing controller code.

BUG=v8:6511
R=fmeawad@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I7c64933d12b2cf53f0636fbc87f6ad5d22019f5c
Reviewed-on: https://chromium-review.googlesource.com/543015
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Fadi Meawad <fmeawad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46118}