We don't currently depend on this, but it might improve performance by
avoiding intermediate copies. The functions are already set up for
perfect forwarding, but without declaring the parameters as forwarding
references, this does not work as expected.

R=ahaas@chromium.org

Change-Id: I2c4d96ea1108b3f884d3e581e74c20aafd232934
Reviewed-on: https://chromium-review.googlesource.com/497409Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45158}