Fix communication with autofill server on iOS

This CL restores the communication of Chrome on iOS with the Autofill
server. It broke by commit fc59bb21
which assigned trusted_params to the network request. However, the
URLLoaderFactory originated from BrowserState and was therefore shared
and not trusted. As per the documentaiton of trusted_params:
"Setting these from an untrusted URLLoader will cause the request to
fail."

This CL removes the trusted_params to bring Autofill back to a working
situation. Maybe the iOS or network stack folks can see whether
we want to have special URLLoaderFactories for components on iOS.
I don't see a precedence for that.

Bug: 1031136
Change-Id: Ic2e04f37f3a30e8adb98e23f19205be09fa5375a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1953707Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722493}

components/autofill/core/browser/autofill_download_manager.cc

@@ -24,6 +24,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "build/build_config.h"
 #include "components/autofill/core/browser/autofill_driver.h"
 #include "components/autofill/core/browser/autofill_metrics.h"
 #include "components/autofill/core/browser/form_structure.h"
@@ -852,9 +853,15 @@ bool AutofillDownloadManager::StartRequest(FormRequestData request_data) {
   resource_request->url = request_url;
   resource_request->credentials_mode = network::mojom::CredentialsMode::kOmit;
   resource_request->method = method;
+
+  // On iOS we have a single, shared URLLoaderFactory provided by BrowserState.
+  // As it is shared, it is not trusted and we cannot assign trusted_params
+  // to the network request.
+#if !defined(OS_IOS)
   resource_request->trusted_params = network::ResourceRequest::TrustedParams();
   resource_request->trusted_params->network_isolation_key =
       driver_->NetworkIsolationKey();
+#endif
 
   // Add Chrome experiment state to the request headers.
   variations::AppendVariationsHeaderUnknownSignedIn(