[CrOS Multidevice] tether::MessageTransferOperation: use the correct Tether feature constant.

This is the correct constant that is expected by host devices.

Bug: 824568, 752273
Change-Id: I7f29159de6eb66f92f4534cd558fe82027175914
Reviewed-on: https://chromium-review.googlesource.com/1105621Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568713}

chromeos/components/tether/message_transfer_operation.cc

@@ -18,6 +18,8 @@ namespace tether {
 
 namespace {
 
+const char kTetherFeature[] = "magic_tether";
+
 cryptauth::RemoteDeviceRefList RemoveDuplicatesFromVector(
     const cryptauth::RemoteDeviceRefList& remote_devices) {
   cryptauth::RemoteDeviceRefList updated_remote_devices;
@@ -148,7 +150,7 @@ void MessageTransferOperation::Initialize() {
               this, remote_device,
               secure_channel_client_->ListenForConnectionFromDevice(
                   remote_device, *device_sync_client_->GetLocalDeviceMetadata(),
-                  "tether", connection_priority_));
+                  kTetherFeature, connection_priority_));
     } else {
       connection_manager_->RegisterRemoteDevice(
           remote_device.GetDeviceId(), request_id_, connection_priority_);

chromeos/components/tether/message_transfer_operation_unittest.cc

@@ -34,6 +34,8 @@ const MessageType kTestMessageType = MessageType::TETHER_AVAILABILITY_REQUEST;
 
 const uint32_t kTestTimeoutSeconds = 5;
 
+const char kTetherFeature[] = "magic_tether";
+
 // A test double for MessageTransferOperation is needed because
 // MessageTransferOperation has pure virtual methods which must be overridden in
 // order to create a concrete instantiation of the class.
@@ -224,6 +226,15 @@ class MessageTransferOperationTest : public testing::Test {
     VerifyOperationStartedAndFinished(false /* has_started */,
                                       false /* has_finished */);
     operation_->Initialize();
+
+    if (base::FeatureList::IsEnabled(chromeos::features::kMultiDeviceApi)) {
+      for (const auto* arguments :
+           fake_secure_channel_client_
+               ->last_listen_for_connection_request_arguments_list()) {
+        EXPECT_EQ(kTetherFeature, arguments->feature);
+      }
+    }
+
     VerifyOperationStartedAndFinished(true /* has_started */,
                                       false /* has_finished */);
   }