Use the UNIMPLEMENTED macro everywhere.

As suggested in review.

Change-Id: Ic14c91a622b545b4800ef021dfb501fb09cbda9d
diff --git a/src/logging.h b/src/logging.h
index 0a96504..bca0cf6 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -113,6 +113,8 @@
 
 #define LG LOG(INFO)
 
+#define UNIMPLEMENTED(level) LOG(level) << __FUNCTION__ << " unimplemented"
+
 class LogMessage {
  public:
   LogMessage(const char* file, int line, LogSeverity severity, int error);