Various logging-related cleanups & reformatting.

These changes were part of the dump-on-DCHECK patch,  (see
https://codereview.chromium.org/1884023002/) but are really just
cleanup/reformatting, so should land separately.  They include
some minor test and formatting changes.

BUG=596231

Review-Url: https://codereview.chromium.org/2712823003
Cr-Commit-Position: refs/heads/master@{#480316}
diff --git a/base/syslog_logging.cc b/base/syslog_logging.cc
index 087b4fd..aff90a4 100644
--- a/base/syslog_logging.cc
+++ b/base/syslog_logging.cc
@@ -12,7 +12,10 @@
 
 #include <windows.h>
 #elif defined(OS_LINUX)
+// <syslog.h> defines a LOG_WARNING macro that could conflict with
+// base::LOG_WARNING.
 #include <syslog.h>
+#undef LOG_WARNING
 #endif
 
 #include <cstring>