Mojom: Blanket change to mark all pointer/handle fields as nullable.

device/serial/data_stream.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module device.serial {
 
 [Client=DataSourceClient]
 interface DataSource {
   // Initializes this DataSource with a data pipe handle to use for data
   // transmission.
-  Init(handle<data_pipe_producer> producer_handle);
+  Init(handle<data_pipe_producer>? producer_handle);
 
   // Resumes sending data after it has been stopped due to an error.
   Resume();
 };
 
 interface DataSourceClient {
   // Invoked to report |error| from the DataSource, at |error_location| bytes
   // into the data stream. No further bytes beyond |error_location| will be
   // transmitted from the DataSource until Resume() is called.
   OnError(uint32 error_location, int32 error);
 };
 
 [Client=DataSinkClient]
 interface DataSink {
   // Initializes this DataSink with a data pipe handle to use for data
   // transmission.
-  Init(handle<data_pipe_consumer> consumer_handle);
+  Init(handle<data_pipe_consumer>? consumer_handle);
 
   // Requests the cancellation of any data that has been written to the pipe,
   // but has not yet been sent to the sink.
   Cancel(int32 error);
 };
 
 interface DataSinkClient {
   // Reports that the sink has successfully received |bytes_sent| bytes of data.
   ReportBytesSent(uint32 bytes_sent);
 
   // Reports that the sink has received |bytes_sent| bytes of data (possibly 0)
   // and encountered an error: |error|. The client should respond with
   // |bytes_to_flush|, the number of bytes enqueued in the data pipe but not yet
   // acked so the correct number of bytes can be flushed from the pipe.
   ReportBytesSentAndError(uint32 bytes_sent, int32 error) => (uint32 bytes_to_flush);
 };
 
 }