Switch usage of _DEBUG macro to NDEBUG.

http://stackoverflow.com/a/29253284/5237416

BUG=None
R=tommi@webrtc.org
NOPRESUBMIT=true

Review URL: https://codereview.webrtc.org/1429513004

Cr-Commit-Position: refs/heads/master@{#10468}
diff --git a/webrtc/base/openssladapter.h b/webrtc/base/openssladapter.h
index 3dcb1c5..cdf45e6 100644
--- a/webrtc/base/openssladapter.h
+++ b/webrtc/base/openssladapter.h
@@ -67,9 +67,9 @@
   static bool VerifyServerName(SSL* ssl, const char* host,
                                bool ignore_bad_cert);
   bool SSLPostConnectionCheck(SSL* ssl, const char* host);
-#if _DEBUG
+#if !defined(NDEBUG)
   static void SSLInfoCallback(const SSL* s, int where, int ret);
-#endif  // !_DEBUG
+#endif
   static int SSLVerifyCallback(int ok, X509_STORE_CTX* store);
   static VerificationCallback custom_verify_callback_;
   friend class OpenSSLStreamAdapter;  // for custom_verify_callback_;