GitLab

As part of a design exploration, it was noted that code in layer.cc is
manually creating a copy of one or more CopyOutputRequests and then
copying over their properties. This is brittle, since adding new
properties to CopyOutputRequest could silently break functionality.

This change solves the problem by adding a "result task runner" that can
be set on a CopyOutputRequest. Using this will ensure results are
delivered via an alternate task runner where that is required. At the
same time, lots of LOC are able to be deleted because the requests are
no longer being duplicated.

Change-Id: Ie26eb2de8f92e796d437e4e1c2b04a964e2ffef7
Reviewed-on: https://chromium-review.googlesource.com/567602Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486030}