Convert //base to use std::unique_ptr

With bonus IWYU fixes that weren't caught by local android gn, cros gn,
linux gn, mac gyp, and win gyp builds.

BUG=554298
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/1852433005

Cr-Commit-Position: refs/heads/master@{#385011}
310 files changed