* 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.cc
content::ResourceContext* resource_context) {
#if defined(USE_NSS_CERTS)
  return std::make_unique<net::ClientCertStoreNSS>(
      net::ClientCertStoreNSS::PasswordDelegateFactory());
#elif defined(OS_WIN)
  return std::make_unique<net::ClientCertStoreWin>();
#elif defined(OS_MACOSX)
  return std::make_unique<net::ClientCertStoreMac>();
#elif defined(USE_OPENSSL)
  return std::unique_ptr<net::ClientCertStore>();
#endif
}
std::unique_ptr<device::LocationProvider>
AtomBrowserClient::OverrideSystemLocationProvider() {
#if BUILDFLAG(OVERRIDE_LOCATION_PROVIDER)
  return std::make_unique<FakeLocationProvider>();
#else
  return nullptr;
#endif
}
network::mojom::NetworkContextPtr AtomBrowserClient::CreateNetworkContext(
    content::BrowserContext* browser_context,
    bool ,
    const base::FilePath& ) {
  if (!browser_context)
    return nullptr;
  return static_cast<AtomBrowserContext*>(browser_context)->GetNetworkContext();
}
void AtomBrowserClient::RegisterOutOfProcessServices(