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### Issue Details

* **Electron Version:** v9.0.0-beta.2, 10.0.0-nightly.20200216
* **Operating System:** Linux
* **Last Known Working Electron version:** 8.0.1

### Expected Behavior
The following text gets printed on screen on "Send cross-domain XHR request" button click:
```
{"status":422,"statusText":"Unprocessable Entity","responseText":"{\"Code\":10080,\"Error\":\"some-user-name@protonmail.ch does not exist. Did you mean SomeUsername@protonmail.com?\",\"ErrorDescription\":\"\",\"Details\":{}}"}
```
![ok](https://user-images.githubusercontent.com/1560781/74688785-cdc9b680-51e9-11ea-9c43-3f06fadee40b.png)

### Actual Behavior
The following text gets printed on screen on "Send cross-domain XHR request" button click:
```
{"status":0,"statusText":"","responseText":"EMPTY"}
XMLHttpRequest error
```
![error](https://user-images.githubusercontent.com/1560781/74688794-d1f5d400-51e9-11ea-93c3-b8a4e427572f.png)

### To Reproduce

https://github.com/vladimiry-playground/electron-quick-start-cors-issue2

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### Screenshots
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### Additional Information

shell/browser/net/proxying_url_loader_factory.cc
mojo_base::BigBuffer data) {
  target_client_->OnReceiveCachedMetadata(std::move(data));
}
void ProxyingURLLoaderFactory::InProgressRequest::OnTransferSizeUpdated(
    int32_t transfer_size_diff) {
  target_client_->OnTransferSizeUpdated(transfer_size_diff);
}
void ProxyingURLLoaderFactory::InProgressRequest::OnStartLoadingResponseBody(
    mojo::ScopedDataPipeConsumerHandle body) {
  target_client_->OnStartLoadingResponseBody(std::move(body));
}
void ProxyingURLLoaderFactory::InProgressRequest::OnComplete(
    const network::URLLoaderCompletionStatus& status) {
  if (status.error_code != net::OK) {
    OnRequestError(status);
    return;
  }
  target_client_->OnComplete(status);
  factory_->web_request_api()->OnCompleted(&info_.value(), request_,
                                           status.error_code);
  
  factory_->RemoveRequest(network_service_request_id_, request_id_);
}
void ProxyingURLLoaderFactory::InProgressRequest::OnLoaderCreated(
    mojo::PendingReceiver<network::mojom::TrustedHeaderClient> receiver) {
  header_client_receiver_.Bind(std::move(receiver));
}
void ProxyingURLLoaderFactory::InProgressRequest::OnBeforeSendHeaders(