ARC: net.mojom passphrase field should be nullable.

components/arc/common/net.mojom

 // Copyright 2015 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 arc.mojom;
 
 [Extensible]
 enum NetworkResult {
   SUCCESS = 0,
   FAILURE = 1,
@@ skipping 12 matching lines @@
   NOT_CONNECTED = 2,
 };
 
 struct VisibleNetworkDetails {
   int32 frequency;
   int32 signal_strength;
   string bssid;
 };
 
 struct ConfiguredNetworkDetails {
-  string passphrase;
+  string? passphrase;
   bool autoconnect;
 };
 
 union NetworkDetails {
   VisibleNetworkDetails visible;
   ConfiguredNetworkDetails configured;
 };
 
 struct WifiConfiguration {
   // These correspond to ONC properties returned by
@@ skipping 60 matching lines @@
   [MinVersion=4] StartDisconnect@8(string guid) => (NetworkResult status);
 };
 
 interface NetInstance {
   // Establishes full-duplex communication with the host.
   Init@0(NetHost host_ptr);
 
   // Notifies the instance of a WiFI AP scan being completed.
   [MinVersion=1] ScanCompleted@1();
 };