This CL replaces occurrences of "length" with the CSA macro
LengthStringConstant().

R=jgruber@chromium.org

Bug: v8:8015
Change-Id: Idf095587940f859e4c634865560abae325cd9fb4
Reviewed-on: https://chromium-review.googlesource.com/1201782Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#55578}