* Output of `node_modules/.bin/electron --version`: **v4.0.0-beta.3**
* Operating System (Platform and Version): **Windows 10**
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): **v3.0.4**

**Expected Behavior**
With electron 3, I could pass `webPreferences: {webwebSecurity: false}` to the BrowserWindow constructor (the equivalent of the `--disable-web-security` Chrome command line argument) which would disable CORB (effectively allowing cross-origin requests).

**Actual behavior**
CORB is still doing its thing (ignoring the `{webwebSecurity: false}` option; I see entries like these in the console:
`Cross-Origin Read Blocking (CORB) blocked cross-origin response <URL> with MIME type application/json. See <URL> for more details.`

**To Reproduce**
Make a request (using fetch or xhr) to a file on a different domain.
Example repo:
```
git clone  https://github.com/IAmPicard/electron-cors-repro
npm install
npm run start
```


atom/browser/atom_browser_client.h
#ifndef ATOM_BROWSER_ATOM_BROWSER_CLIENT_H_
#define ATOM_BROWSER_ATOM_BROWSER_CLIENT_H_
#include <map>
#include <memory>
#include <set>
#include <string>
#include <vector>
#include "content/public/browser/content_browser_client.h"
#include "content/public/browser/render_process_host_observer.h"
#include "net/ssl/client_cert_identity.h"
namespace content {
class QuotaPermissionContext;
class ClientCertificateDelegate;
}  
namespace net {
class SSLCertRequestInfo;
}
namespace atom {
class AtomResourceDispatcherHostDelegate;
class NotificationPresenter;