Change more base::ListValue methods to use std::unique_ptr.

AppendIfNotPresent() and Insert() now take unique_ptr instead of a raw
pointer.

BUG=581865
TBR=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2336863003
Cr-Commit-Position: refs/heads/master@{#418494}
30 files changed