Also add a helper class to keep the previous behaviour of
automatically appending a newline after every new message.

BUG=angleproject:992

Change-Id: I0ff5d2846175cf19de7a6af295af24a92451456f
Reviewed-on: https://chromium-review.googlesource.com/268744Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>