Replace scoped_ptr with unique_ptr in webrtc/base/

This propagated into various other places. Also had to #include headers that
were implicitly pulled by "scoped_ptr.h".

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1920043002

Cr-Original-Commit-Position: refs/heads/master@{#12501}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 555604a7463c6a6677f54aff340e7852a16b3c58
116 files changed