Make some fields non-nullable in serial.mojom and data_stream.mojom.

device/serial/serial.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.
 
 import "data_stream.mojom"
 
 module device.serial {
 
 struct DeviceInfo {
-  string? path;
+  string path;
   uint16 vendor_id;
   bool has_vendor_id = false;
   uint16 product_id;
   bool has_product_id = false;
   string? display_name;
 };
 
 enum SendError {
   NONE,
   DISCONNECTED,
@@ skipping 54 matching lines @@
 };
 
 struct DeviceControlSignals {
   bool dcd;
   bool cts;
   bool ri;
   bool dsr;
 };
 
 interface SerialService {
-  GetDevices() => (DeviceInfo?[]? devices);
+  GetDevices() => (DeviceInfo[] devices);
 
   // Creates a |Connection| to |path| with options specified by |options|,
   // returning it via |connection|. Sending and receiving data over this
   // connection is handled by |sink| and |source|, respectively. This will fail
   // and |connection| will not be usable if |path| does not specify a valid
   // serial device or there is an error connecting to or configuring the
   // connection.
-  Connect(string? path,
+  Connect(string path,
           ConnectionOptions? options,
-          Connection&? connection,
-          DataSink&? sink,
-          DataSource&? source);
+          Connection& connection,
+          DataSink& sink,
+          DataSource& source);
 };
 
 interface Connection {
   GetInfo() => (ConnectionInfo? info);
-  SetOptions(ConnectionOptions? options) => (bool success);
-  SetControlSignals(HostControlSignals? signals) => (bool success);
+  SetOptions(ConnectionOptions options) => (bool success);
+  SetControlSignals(HostControlSignals signals) => (bool success);
   GetControlSignals() => (DeviceControlSignals? signals);
   Flush() => (bool success);
 };
 
 }