* 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 content::HostZoomMap::ZoomLevelChange& change) {
  if (change.mode == content::HostZoomMap::ZOOM_CHANGED_FOR_HOST) {
    auto it = host_zoom_factor_.find(change.host);
    if (it == host_zoom_factor_.end())
      return;
    host_zoom_factor_.insert(
        it, std::make_pair(change.host,
                           content::ZoomLevelToZoomFactor(change.zoom_level)));
  }
}
}