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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
v8::Local<v8::Context> context,
    int world_id) {
  if (ShouldNotifyClient(world_id))
    renderer_client_->WillReleaseScriptContext(context, render_frame_);
}
void AtomRenderFrameObserver::OnDestruct() {
  delete this;
}
void AtomRenderFrameObserver::CreateIsolatedWorldContext() {
  auto* frame = render_frame_->GetWebFrame();
  
  
  frame->SetIsolatedWorldHumanReadableName(
      World::ISOLATED_WORLD,
      blink::WebString::FromUTF8("Electron Isolated Context"));
  
  frame->SetIsolatedWorldSecurityOrigin(
      World::ISOLATED_WORLD, frame->GetDocument().GetSecurityOrigin());
  
  blink::WebScriptSource source("void 0");
  frame->ExecuteScriptInIsolatedWorld(World::ISOLATED_WORLD, source);
}
bool AtomRenderFrameObserver::IsMainWorld(int world_id) {