* Electron version: 1.6.1
* Operating system: macOS 10.12.3, Windows 7 64bit

### Expected behavior

Should emit an error on the request object.

### Actual behavior

<img width="420" alt="image" src="https://cloud.githubusercontent.com/assets/99662/23713890/4e9b8f52-041f-11e7-9dfb-e8408bb58670.png">

An uncatchable error happens.

### How to reproduce
```bash
git clone https://github.com/arantes555/electron-net-encoding-testcase.git
cd electron-net-encoding-testcase
npm install
npm start
```

atom/browser/net/atom_url_request.cc
DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
  if (!request_) {
    return;
  }
  request_->CancelAuth();
}
void AtomURLRequest::DoCancelWithError(const std::string& error,
                                       bool isRequestError) {
  DoCancel();
  content::BrowserThread::PostTask(
      content::BrowserThread::UI, FROM_HERE,
      base::Bind(&AtomURLRequest::InformDelegateErrorOccured, this, error,
                 isRequestError));
}
void AtomURLRequest::DoSetLoadFlags(int flags) const {
  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
  if (!request_) {
    return;
  }
  request_->SetLoadFlags(request_->load_flags() | flags);
}
void AtomURLRequest::OnAuthRequired(net::URLRequest* request,
                                    net::AuthChallengeInfo* auth_info) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
  content::BrowserThread::PostTask(
      content::BrowserThread::UI, FROM_HERE,
      base::Bind(&AtomURLRequest::InformDelegateAuthenticationRequired, this,
                 scoped_refptr<net::AuthChallengeInfo>(auth_info)));
}
void AtomURLRequest::OnResponseStarted(net::URLRequest* request) {