Pass the protocol handlers passed from StoragePartitionImpMap to URLRequestContextBuilder.

Change-Id: If94a0bfa08381a856e7ba682cbd5b85971ed1eac
Reviewed-on: https://chromium-review.googlesource.com/c/1282210Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Johnny Ding <jnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600072}

headless/lib/browser/headless_request_context_manager.cc

@@ -357,6 +357,11 @@ void HeadlessRequestContextManager::InitializeOnIO() {
     builder->SetCreateHttpTransactionFactoryCallback(
         base::BindOnce(&content::CreateDevToolsNetworkTransactionFactory));
     builder->SetInterceptors(std::move(request_interceptors_));
+    for (auto& protocol_handler : protocol_handlers_) {
+      builder->SetProtocolHandler(protocol_handler.first,
+                                  std::move(protocol_handler.second));
+    }
+    protocol_handlers_.clear();
 
     net::URLRequestContext* url_request_context = nullptr;
     network_context_owner_ =