Use std::unique_ptr instead of UniquePtr.

We're deprecating UniquePtr, so we need to move to the real thing.

Bug: http://b/22403888
Change-Id: I5b7fdf4924dd8c12a8c7dba89278714ca6fdc60a
(cherry picked from commit b0624da1181276ff4caa5e57a7a4abf766902e3e)
2 files changed