make pulseaudio available for all posix platforms because it's not linux only

media/base/media_switches.cc

Index: media/base/media_switches.cc
diff --git a/media/base/media_switches.cc b/media/base/media_switches.cc
index eb57065db099d07835cebe1488d0b9e7dc51c628..bd2438db5de1356931440338bf30e505bb2cd581 100644
--- a/media/base/media_switches.cc
+++ b/media/base/media_switches.cc
@@ -13,8 +13,10 @@ const char kAlsaOutputDevice[] = "alsa-output-device";
 const char kAlsaInputDevice[] = "alsa-input-device";
 #endif
 
-// Use PulseAudio instead of ALSA on Linux.
+// Use PulseAudio on platforms that support it.
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
 const char kUsePulseAudio[] = "use-pulseaudio";
+#endif
 
 // Set number of threads to use for video decoding.
 const char kVideoThreads[] = "video-threads";