Use base::Value::ToUniquePtrValue() where appropriate.

Make it obvious its converting an existing base::Value to a different
form. Also change some potential ToUniquePtrValue() calls to the new
base::Value API instead, and avoid some base::Value::Clone() calls.

BUG=646113

Change-Id: I05a457b42580ac5059d8f63cd1977ec7339a1cf5
Reviewed-on: https://chromium-review.googlesource.com/732343
Reviewed-by: Jan Wilken Dörrie <[email protected]>
Reviewed-by: Istiaque Ahmed <[email protected]>
Reviewed-by: Colin Blundell <[email protected]>
Commit-Queue: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#511928}
8 files changed