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_unittest.cc

@@ -88,14 +88,6 @@ TEST(ConfigParser, ParseConfig) {
   EXPECT_EQ(true, parser.Parse(&key_val_pairs));
 }
 
-#if !defined(WEBRTC_CHROMIUM_BUILD)
-TEST(ReadLinuxLsbRelease, ReturnsSomething) {
-  std::string str = ReadLinuxLsbRelease();
-  // ChromeOS don't have lsb_release
-  // EXPECT_FALSE(str.empty());
-}
-#endif
-
 TEST(ReadLinuxUname, ReturnsSomething) {
   std::string str = ReadLinuxUname();
   EXPECT_FALSE(str.empty());