When internalizing string literals (for quoted strings or property names),
try to create a sliced string of the source string rather than allocating
a copy of the bytes.

This will not work for string literals that contain escapes (e.g. unicode
escapes), and currently does not support two-byte strings.

Bug: chromium:818642
Change-Id: I686e5ad36baecd1a84ce5e124118431249b6c980
Reviewed-on: https://chromium-review.googlesource.com/1010282Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52898}