Enable size_t to int truncation warnings in PPAPI

ppapi/tests/test_tcp_socket_private.cc

Index: ppapi/tests/test_tcp_socket_private.cc
diff --git a/ppapi/tests/test_tcp_socket_private.cc b/ppapi/tests/test_tcp_socket_private.cc
index d3efbe335d514ec1c3b105a9a892060b295f2d5f..0d43a764c304958d80380138cbf68c5bffe54f4d 100644
--- a/ppapi/tests/test_tcp_socket_private.cc
+++ b/ppapi/tests/test_tcp_socket_private.cc
@@ -246,7 +246,8 @@ int32_t TestTCPSocketPrivate::WriteStringToSocket(pp::TCPSocketPrivate* socket,
   size_t written = 0;
   while (written < s.size()) {
     TestCompletionCallback cb(instance_->pp_instance(), callback_type());
-    int32_t rv = socket->Write(buffer + written, s.size() - written,
+    int32_t rv = socket->Write(buffer + written,
+                               static_cast<int32_t>(s.size() - written),
                                cb.GetCallback());
     if (callback_type() == PP_REQUIRED && rv != PP_OK_COMPLETIONPENDING)
       return PP_ERROR_FAILED;