Improvements to rtc::Bind

BUG=webrtc:4690

Support for rtc::scoped_ptr as return type.
Support for up to 6 input parameters.

R=pthatcher@webrtc.org, solenberg@webrtc.org

Review URL: https://codereview.webrtc.org/1226153003 .

Cr-Commit-Position: refs/heads/master@{#9569}
2 files changed