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-Commit-Position: refs/heads/master@{#9273}

webrtc/base/linux.h

@@ -104,11 +104,6 @@ class ProcCpuInfo {
   ConfigParser::MapVector sections_;
 };
 
-#if !defined(WEBRTC_CHROMIUM_BUILD)
-// Builds a string containing the info from lsb_release on a single line.
-std::string ReadLinuxLsbRelease();
-#endif
-
 // Returns the output of "uname".
 std::string ReadLinuxUname();