[remoting][IT2ME] Fix crash on the non-proxied signaling path

Turns out I just accidentally deleted the register_request creation
code.

Bug: 1103416
Change-Id: I99e0a8e54be01ebe3aef29e1051840b36a1277d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2318051
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Auto-Submit: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791434}

remoting/host/it2me/it2me_native_messaging_host.cc

@@ -287,6 +287,10 @@ void It2MeNativeMessagingHost::ProcessConnect(
           },
           username, access_token);
 
+      register_host_request =
+          std::make_unique<RemotingRegisterSupportHostRequest>(
+              std::make_unique<PassthroughOAuthTokenGetter>(username,
+                                                            access_token));
       log_to_server = std::make_unique<RemotingLogToServer>(
           ServerLogEntry::IT2ME, std::make_unique<PassthroughOAuthTokenGetter>(
                                      username, access_token));