In these cases the std::function state does not change, hence, it can be
a const ref. Fixing clang-tidy warning.

Bug: v8:8015
Change-Id: I221b0c3e18c5c1f54d35d671445d2e947cf64c02
Reviewed-on: https://chromium-review.googlesource.com/1209822
Commit-Queue: Florian Sattler <sattlerf@google.com>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55712}