It's OS_MACOSX, not OS_MAC.

chrome/browser/ui/media_stream_infobar_delegate.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <functional>
 
 #include "base/logging.h"
 #include "chrome/browser/ui/media_stream_infobar_delegate.h"
 #include "content/public/common/media_stream_request.h"
@@ skipping 92 matching lines @@
     content::MediaStreamDevices::const_iterator it = std::find_if(
         device_it->second.begin(), device_it->second.end(), DeviceIdEquals(id));
     if (it != device_it->second.end())
       devices->push_back(*it);
   }
 }
 
 // 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
   // we don't want WebRTC to be waiting for an answer that will never come.
   Deny();
 }
 
 gfx::Image* MediaStreamInfoBarDelegate::GetIcon() const {
   return &ResourceBundle::GetSharedInstance().GetNativeImageNamed(has_video_ ?
       IDR_INFOBAR_MEDIA_STREAM_CAMERA : IDR_INFOBAR_MEDIA_STREAM_MIC);
 }
 
 InfoBarDelegate::Type MediaStreamInfoBarDelegate::GetInfoBarType() const {
   return PAGE_ACTION_TYPE;
 }
 
 MediaStreamInfoBarDelegate*
     MediaStreamInfoBarDelegate::AsMediaStreamInfobarDelegate() {
   return this;
 }