libweave: base::Value refactor (1/n)

Rename unit test utility test::CreateValue to test::CreateUniquePtrValue
so that (in next CL of the series) I will add base::CreateValue which
returns a base::Value directly (not wrapped in std::unique_ptr).
test::CreateUniquePtrValue is only kept for the migration and should be
removed eventually.

BUG=chromium:1099111
TEST=FEATURES=test emerge-hatch libweave

Change-Id: Icfde0cb7cbc77c6b2085245f348f8ff07a0a66e1
Reviewed-on: https://chromium-review.googlesource.com/c/weave/libweave/+/3312867
Tested-by: Grace Cham <hscham@chromium.org>
Reviewed-by: Qijiang YĆ«ki Ishii <fqj@google.com>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Grace Cham <hscham@chromium.org>
8 files changed