Make POSIX SIGTERM/SIGINT/SIGHUP handler async signal safe.

base/logging.h

Index: base/logging.h
diff --git a/base/logging.h b/base/logging.h
index 4fbe4830f28b7fb9ce4ccb79b8ebce6c5809a7f0..cac9ca34cb1c40ef7d9cf0265007fc362d9a7a5e 100644
--- a/base/logging.h
+++ b/base/logging.h
@@ -772,6 +772,17 @@ class ErrnoLogMessage {
 //       after this call.
 void CloseLogFile();
 
+// Async signal safe logging mechanism.
+void RawLog(int level, const char* message);
+
+#define RAW_LOG(level, message) logging::RawLog(logging::LOG_ ## level, message)
+
+#define RAW_CHECK(condition)                                                   \
+  do {                                                                         \
+    if (!(condition))                                                          \
+      logging::RawLog(logging::LOG_FATAL, "Check failed: " #condition "\n");   \
+  } while (0)
+
 }  // namespace logging
 
 // These functions are provided as a convenience for logging, which is where we