libvpx's UNUSED macro conflicts with webrtc/base's. Added missing include of assert.h. Globally defined function "Unused" in talk/base and its copy (webrtc/base) is causing a conflict.

libvpx macro (UNUSED) can be found here:
http://src.chromium.org/viewvc/chrome/trunk/deps/third_party/libvpx/source/libvpx/vpx/vpx_codec.h

BUG=N/A
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/17489004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6185 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/audio_device/android/single_rw_fifo.cc

@@ -10,6 +10,8 @@
 
 #include "webrtc/modules/audio_device/android/single_rw_fifo.h"
 
+#include <assert.h>
+
 static int UpdatePos(int pos, int capacity) {
   return (pos + 1) % capacity;
 }