Switch usage of _DEBUG macro to NDEBUG.

webrtc/base/logging.cc

Index: webrtc/base/logging.cc
diff --git a/webrtc/base/logging.cc b/webrtc/base/logging.cc
index b02be27e33a42e009301fb59b538bb976b7423c4..686b9b2b02b482e104f7daab6eb5f4bde336821d 100644
--- a/webrtc/base/logging.cc
+++ b/webrtc/base/logging.cc
@@ -92,13 +92,13 @@ std::string ErrorName(int err, const ConstantLabel* err_table) {
 /////////////////////////////////////////////////////////////////////////////
 
 // By default, release builds don't log, debug builds at info level
-#if _DEBUG
+#if !defined(NDEBUG)
 LoggingSeverity LogMessage::min_sev_ = LS_INFO;
 LoggingSeverity LogMessage::dbg_sev_ = LS_INFO;
-#else  // !_DEBUG
+#else
 LoggingSeverity LogMessage::min_sev_ = LS_NONE;
 LoggingSeverity LogMessage::dbg_sev_ = LS_NONE;
-#endif  // !_DEBUG
+#endif
 bool LogMessage::log_to_stderr_ = true;
 
 namespace {
@@ -340,7 +340,7 @@ void LogMessage::OutputToDebug(const std::string& str,
                                LoggingSeverity severity,
                                const std::string& tag) {
   bool log_to_stderr = log_to_stderr_;
-#if defined(WEBRTC_MAC) && !defined(WEBRTC_IOS) && (!defined(_DEBUG) || defined(NDEBUG))
+#if defined(WEBRTC_MAC) && !defined(WEBRTC_IOS) && defined(NDEBUG)
   // On the Mac, all stderr output goes to the Console log and causes clutter.
   // So in opt builds, don't log to stderr unless the user specifically sets
   // a preference to do so.