[logdog] Don't do extra string copy when printing lines
[logdog] Don't do extra string copy when printing lines

This should be a strictly faster version of the same behavior.

Change-Id: I2eabd6c9e11d725af61c1a4daa2d18f9a9ff4785
Reviewed-on: https://chromium-review.googlesource.com/c/1289234
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go