Embedders should implement them via the v8::TracingController interface
and return a pointer to an instance of that interface from
v8::Platform::GetTracingController

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

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: If17b013c7ce4cf540a186767fd6e1b5e00e0dab2
Reviewed-on: https://chromium-review.googlesource.com/554770Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47549}