[WebOTP] Use correct variable and avoid a crash

Test: `./chrome --enable-features=WebID https://webid-demo.glitch.me` no longer crashes
Bug: None
Change-Id: I1a7f0fd7f1d9e0a73960be223daf6a238140b11e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2585835
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835988}

content/browser/webid/federated_auth_request_impl.cc

@@ -261,7 +261,7 @@ std::unique_ptr<WebContents> FederatedAuthRequestImpl::CreateIdpWebContents() {
   // Store the callback on the provider web contents so that it can be
   // used later.
   IdTokenRequestCallbackData::Set(
-      idp_web_contents_.get(),
+      idp_web_contents.get(),
       base::BindOnce(&FederatedAuthRequestImpl::OnTokenProvided,
                      weak_ptr_factory_.GetWeakPtr()));
   return idp_web_contents;