Make //crypto factories return std::unique_ptr<>s

Rather than make callers use base::WrapUnique or .reset(),
have //crypto functions that create new instances return them
in std::unique_ptr<>s

Also fixup NULL vs nullptr where it matters most, and remove
superflous .get() tests from the unique_ptr<>s

BUG=none
R=davidben@chromium.org

Review-Url: https://codereview.chromium.org/2095523002
Cr-Commit-Position: refs/heads/master@{#402368}
44 files changed