Remove SendBeacon body size counting logic

It's replaced with the "keepalive" logic in ResourceFetcher.

Bug: 695939
Change-Id: I788423d057b73becaed60932a176fa987d27e7c3
Reviewed-on: https://chromium-review.googlesource.com/838767
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525920}
5 files changed