Mojo C++ bindings: switch device/serial mojom target to use STL types.

device/serial/serial_device_enumerator_linux.cc

Index: device/serial/serial_device_enumerator_linux.cc
diff --git a/device/serial/serial_device_enumerator_linux.cc b/device/serial/serial_device_enumerator_linux.cc
index 5b0faf21c6af4685e554f3305e372cb718847c48..dbeccecb8636e342a05d3415ae8531b5c7514aed 100644
--- a/device/serial/serial_device_enumerator_linux.cc
+++ b/device/serial/serial_device_enumerator_linux.cc
@@ -87,7 +87,7 @@ mojo::Array<serial::DeviceInfoPtr> SerialDeviceEnumeratorLinux::GetDevices() {
         info->has_product_id = true;
       }
       if (product_name)
-        info->display_name = product_name;
+        info->display_name.emplace(product_name);
       devices.push_back(std::move(info));
     }
   }