Move scoped_ptr "free" functions into the webrtc namespace.

Resolves a conflict with Chromium's scoped_ptr on the recently added
make_scoped_ptr().

TEST=local Chromium Linux build passes.
R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/26969004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7535 4adac7df-926f-26a2-2b94-8c16560cd09d