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* Electron version: 1.7.2
* Operating system: macOS Sierra

### Expected behavior

Webview appear

### Actual behavior

It don't

### How to reproduce

1. Create a browser window with contextIsolation on true and webviewTag on true
2. Inside of it, add a webview
3. Run it, webview should not appear

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atom/renderer/atom_render_frame_observer.cc
document_created_ = true;
}
void AtomRenderFrameObserver::DidCreateScriptContext(
    v8::Handle<v8::Context> context,
    int world_id) {
  if (ShouldNotifyClient(world_id))
    renderer_client_->DidCreateScriptContext(context, render_frame_);
  if (renderer_client_->isolated_world() && IsMainWorld(world_id) &&
      render_frame_->IsMainFrame()) {
    CreateIsolatedWorldContext();
    renderer_client_->SetupMainWorldOverrides(context);
  }
}
void AtomRenderFrameObserver::DraggableRegionsChanged() {
  blink::WebVector<blink::WebDraggableRegion> webregions =
      render_frame_->GetWebFrame()->GetDocument().DraggableRegions();
  std::vector<DraggableRegion> regions;
  for (auto& webregion : webregions) {
    DraggableRegion region;
    render_frame_->GetRenderView()->ConvertViewportToWindowViaWidget(
        &webregion.bounds);
    region.bounds = webregion.bounds;
    region.draggable = webregion.draggable;
    regions.push_back(region);
  }
  Send(new AtomFrameHostMsg_UpdateDraggableRegions(routing_id(), regions));
}
void AtomRenderFrameObserver::WillReleaseScriptContext(