Fix Windows build. %zu isn't supported in the crt implementation

we use there, so it just crashes.
Review URL: http://webrtc-codereview.appspot.com/213001

git-svn-id: http://webrtc.googlecode.com/svn/trunk@712 4adac7df-926f-26a2-2b94-8c16560cd09d

peerconnection/samples/server/utils.cc

@@ -17,3 +17,14 @@ std::string int2str(int i) {
   sprintf(buffer, "%d", i);  // NOLINT
   return buffer;
 }
+
+std::string size_t2str(size_t i) {
+  char buffer[32] = {0};
+#ifdef WIN32
+  // %zu isn't supported on Windows.
+  sprintf(buffer, "%Iu", i);  // NOLINT
+#else
+  sprintf(buffer, "%zu", i);  // NOLINT
+#endif
+  return buffer;
+}