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/webrtc@6185 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/base/httpserver.cc b/base/httpserver.cc
index caa58ef..0d22584 100644
--- a/base/httpserver.cc
+++ b/base/httpserver.cc
@@ -222,7 +222,7 @@
 
 void
 HttpServer::Connection::onHttpClosed(HttpError err) {
-  UNUSED(err);
+  RTC_UNUSED(err);
   server_->Remove(connection_id_);
 }