* Electron version: 1.6.1
* Operating system: MacOS 10.12

Create a webview, set the zoom level, then create a second webview for content at the same domain as the 1st webview.

### Expected behavior

Ideally the second webview would assume the same zoom as the existing webview. At minumum, it'd be good if the first webview maintained its current zoom.

### Actual behavior

The zoom level is reset on both webviews.

### How to reproduce

https://github.com/pfrazee/electron-bug-webview-zoom Instructions on the readme
atom/browser/web_contents_zoom_controller.cc
const GURL& url) {
  if (content::ZoomValuesEqual(GetDefaultZoomFactor(), content::kEpsilon))
    return;
  if (host_zoom_map_->UsesTemporaryZoomLevel(old_process_id_, old_view_id_)) {
    host_zoom_map_->ClearTemporaryZoomLevel(old_process_id_, old_view_id_);
  }
  if (embedder_zoom_controller_ &&
      embedder_zoom_controller_->UsesTemporaryZoomLevel()) {
    double level = embedder_zoom_controller_->GetZoomLevel();
    SetTemporaryZoomLevel(level);
    return;
  }
  
  
  
  
  std::string host = net::GetHostOrSpecFromURL(url);
  double zoom_factor = GetDefaultZoomFactor();
  auto it = host_zoom_factor_.find(host);
  if (it != host_zoom_factor_.end())
    zoom_factor = it->second;
  auto level = content::ZoomFactorToZoomLevel(zoom_factor);
  if (content::ZoomValuesEqual(level, GetZoomLevel()))
    return;
  SetZoomLevel(level);
}
void WebContentsZoomController::OnZoomLevelChanged(