In order to limit the overall length of error message, limit the output
of string provided by the user. This is implemented by a helper class
which takes the maximum length as template argument and has simple
accessors for the start address and the length of the truncated string.

This is the compromise CL after
https://chromium-review.googlesource.com/c/566815 and
https://chromium-review.googlesource.com/c/594288.

R=titzer@chromium.org

Bug: chromium:740023, chromium:749041, v8:6634
Change-Id: I7c154eb18b3a6befd5ecabbd2f435b015ad71542
Reviewed-on: https://chromium-review.googlesource.com/600547Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47157}