Cherrypick of r34036 to make merge at r34474 build....

base/logging.h

Index: base/logging.h
===================================================================
--- base/logging.h	(revision 34497)
+++ base/logging.h	(working copy)
@@ -765,6 +765,17 @@
 //       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