* Output of `node_modules/.bin/electron --version`: v5.0.0-nightly.20190107
* Operating System (Platform and Version): macOS Mojave 10.14.2 (18C54)
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): never

**Expected Behavior**
Using navigator.mediaDevices.getDisplayMedia({ video: true }), a native screen picker should appear.

**Actual behavior**
The following error is thrown: NotAllowedError: Permission denied

**Screenshots**
Expected dialog
![image](https://user-images.githubusercontent.com/1120050/51625551-71736500-1f0b-11e9-9a95-1406cad95046.png)
atom/browser/atom_browser_client.cc
content::BrowserContext* browser_context,
    const GURL& url,
    content::RenderFrameHost* rfh) const {
  std::string affinity = GetAffinityPreference(rfh);
  if (!affinity.empty()) {
    auto iter = site_per_affinities_.find(affinity);
    GURL dest_site = content::SiteInstance::GetSiteForURL(browser_context, url);
    if (iter != site_per_affinities_.end() &&
        IsSameWebSite(browser_context, iter->second->GetSiteURL(), dest_site)) {
      return iter->second;
    }
  }
  return nullptr;
}
void AtomBrowserClient::ConsiderSiteInstanceForAffinity(
    content::RenderFrameHost* rfh,
    content::SiteInstance* site_instance) {
  std::string affinity = GetAffinityPreference(rfh);
  if (!affinity.empty()) {
    site_per_affinities_[affinity] = site_instance;
  }
}
void AtomBrowserClient::RenderProcessWillLaunch(