* 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::RenderFrameHost* render_frame_host,
    content::BrowserContext* browser_context,
    content::SiteInstance* current_instance,
    const GURL& url) {
  if (url.SchemeIs(url::kJavaScriptScheme))
    
    return false;
  int process_id = current_instance->GetProcess()->GetID();
  if (!IsRendererSandboxed(process_id)) {
    if (!RendererUsesNativeWindowOpen(process_id)) {
      
      
      return true;
    }
    auto* web_contents =
        content::WebContents::FromRenderFrameHost(render_frame_host);
    if (!ChildWebContentsTracker::FromWebContents(web_contents)) {
      
      
      
      
      return true;
    }
  }
  
  auto src_url = current_instance->GetSiteURL();
  return !IsSameWebSite(browser_context, src_url, url);
}
void AtomBrowserClient::AddProcessPreferences(