Use base::WrapUnique in CanonicalCookie factory methods.

This is part of an effort to make CanonicalCookie's constructor private.

Since make_unique<T> will not compile if T's constructor is private, we
need to replace uses of make_unique in CanonicalCookie's implementation
with base::WrapUnique() and the "new" keyword.

Bug: 1102874
Change-Id: Ie5de0b4814cd8c39c5ff7484f2a8f880f2ec810d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2559287
Reviewed-by: Maksim Orlovich <morlovich@chromium.org>
Commit-Queue: Dylan Cutler <dylancutler@google.com>
Cr-Commit-Position: refs/heads/master@{#831075}