This patch removes unnecessary copies and adds reserves to vectors that
are filled in a loop afterwards. Fixing clang-tidy warning.

Bug: v8:8015
Change-Id: I4e13c0445a9760e09ef03a62ae48be622ebecc6b
Reviewed-on: https://chromium-review.googlesource.com/1209783Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#55776}