GitLab

This is needed because of how argument-dependent lookup works (it
looks in the namespace of the type for an unqualified function name).

According to go/using-std-swap, the recommended usage pattern is:
  using std::swap;
  swap(thing1, thing2);
Having swap outside of base namespace wouldn't work with this
recommendation as slower std::swap would be silently used instead.

Bug: 1073933
Change-Id: Ib4485b51ba52ad491306bec9b4402a154adae16c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2167796
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763350}