Use scoped_ptr for ThreadWrapper::CreateThread.

BUG=
R=henrika@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45799004

Cr-Original-Commit-Position: refs/heads/master@{#8794}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 361981faa86668cd9b20a2837d0b166fc024cd9b
67 files changed