This change allows passing no context to NewConsString,
since it's not used anyway.

Change-Id: I125e1dca90ff1b8d1c8695d5b688e8ff4e075044
Reviewed-on: https://chromium-review.googlesource.com/1190602
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55440}