It's OS_MACOSX, not OS_MAC.

chrome/browser/ui/media_stream_infobar_delegate.cc

Index: chrome/browser/ui/media_stream_infobar_delegate.cc
diff --git a/chrome/browser/ui/media_stream_infobar_delegate.cc b/chrome/browser/ui/media_stream_infobar_delegate.cc
index 56ab12fc09f25818725af485b330e21d6ee9eeed..d732a0b041eb3b757ab03c847aaf8a1079a45bc3 100644
--- a/chrome/browser/ui/media_stream_infobar_delegate.cc
+++ b/chrome/browser/ui/media_stream_infobar_delegate.cc
@@ -110,14 +110,14 @@ void MediaStreamInfoBarDelegate::AddDeviceWithId(
 // MediaStreamInfoBarDelegate::CreateInfoBar is implemented in platform-specific
 // files.
 
-#if defined(OS_MAC)
+#if defined(OS_MACOSX)
 // TODO(macourteau): This section is temporary, until the InfoBar is implemented
 // on MacOS, to make sure everything compiles and links.
 InfoBar* MediaStreamInfoBarDelegate::CreateInfoBar(InfoBarTabHelper* owner) {
   DCHECK(owner);
   return NULL;
 }
-#endif  // OS_MAC
+#endif  // OS_MACOSX
 
 void MediaStreamInfoBarDelegate::InfoBarDismissed() {
   // Deny the request if the infobar was closed with the 'x' button, since