Allow SendMessage callers to decide whether to copy or move message data, depends on whether the passed down MemSlices are reference-counted or copy-on-demand.

Merge internal change: 232532630

R=rch@chromium.org

Change-Id: I09af6bbc6180d4b64cbb2a11b4ec94c714ebb838
Reviewed-on: https://chromium-review.googlesource.com/c/1456497
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Fan Yang <fayang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629693}
23 files changed