"short" external strings are not short, they mean that the external data
pointer is not cached. Rename the various classes and objects to align
with the actual meaning.

Bug: chromium:877044
Change-Id: Ie3d5baa9ad352ac6ca89f5ba1d066760825e4beb
Reviewed-on: https://chromium-review.googlesource.com/1185192Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55432}