Some cleanup for base/logging and base/stream.h

* Fix race when calling UpdateMinLogSeverity
* Remove unused 'diagnostic mode'
* Remove LogToStream
* Fix ctor of StringStream
* Delete POpenStream
* Delete AsyncWriteStream
* Delete CircularFileStream
* Delete StreamSegment

BUG=
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/57429004

Cr-Original-Commit-Position: refs/heads/master@{#9273}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 00aac5aacfa1778cafa1a67036743df990e21153
12 files changed