Hide syslog's LOG_INFO from the rest of the code

Both syslog and the base namespace have LOG_INFO symbols and
in certain cases (which include, but is not limited to,
jumbo builds) those will clash.

This patch undefs the syslog LOG_INFO macro
as is already done with LOG_WARNING previously.

Change-Id: Iff59a2ef079d3bb38378af76932b21a128507353
Reviewed-on: https://chromium-review.googlesource.com/1027611
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574103}

base/syslog_logging.cc

@@ -10,9 +10,10 @@
 #include "base/callback_helpers.h"
 #include "base/debug/stack_trace.h"
 #elif defined(OS_LINUX)
-// <syslog.h> defines a LOG_WARNING macro that could conflict with
-// base::LOG_WARNING.
+// <syslog.h> defines LOG_INFO, LOG_WARNING macros that could conflict with
+// base::LOG_INFO, base::LOG_WARNING.
 #include <syslog.h>
+#undef LOG_INFO
 #undef LOG_WARNING
 #endif