Test that base::span<> is compatible with gmock macros.

Show that base::span<> can be used against other common types in
the ElementsAre()/ElementsAreArray() matchers.

Change-Id: I45dc4e925ddf208b87acbc139f8c2f8feb84bb16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5607486
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312177}