* 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
void ResourceDispatcherHostCreated() override;
  bool CanCreateWindow(content::RenderFrameHost* opener,
                       const GURL& opener_url,
                       const GURL& opener_top_level_frame_url,
                       const GURL& source_origin,
                       content::mojom::WindowContainerType container_type,
                       const GURL& target_url,
                       const content::Referrer& referrer,
                       const std::string& frame_name,
                       WindowOpenDisposition disposition,
                       const blink::mojom::WindowFeatures& features,
                       const std::vector<std::string>& additional_features,
                       const scoped_refptr<network::ResourceRequestBody>& body,
                       bool user_gesture,
                       bool opener_suppressed,
                       bool* no_javascript_access) override;
  void GetAdditionalAllowedSchemesForFileSystem(
      std::vector<std::string>* additional_schemes) override;
  void GetAdditionalWebUISchemes(
      std::vector<std::string>* additional_schemes) override;
  void SiteInstanceDeleting(content::SiteInstance* site_instance) override;
  std::unique_ptr<net::ClientCertStore> CreateClientCertStore(
      content::ResourceContext* resource_context) override;
  std::unique_ptr<device::LocationProvider> OverrideSystemLocationProvider()
      override;
  network::mojom::NetworkContextPtr CreateNetworkContext(
      content::BrowserContext* browser_context,
      bool in_memory,
      const base::FilePath& relative_partition_path) override;
  void RegisterOutOfProcessServices(OutOfProcessServiceMap* services) override;