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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_renderer_client.h
}
namespace atom {
class AtomBindings;
class NodeBindings;
class AtomRendererClient : public RendererClientBase {
 public:
  AtomRendererClient();
  ~AtomRendererClient() override;
  
  void DidCreateScriptContext(v8::Handle<v8::Context> context,
                              content::RenderFrame* render_frame) override;
  void WillReleaseScriptContext(v8::Handle<v8::Context> context,
                                content::RenderFrame* render_frame) override;
  void SetupMainWorldOverrides(v8::Handle<v8::Context> context) override;
 private:
  enum NodeIntegration {
    ALL,
    EXCEPT_IFRAME,
    MANUAL_ENABLE_IFRAME,
    DISABLE,
  };
  
  void RenderThreadStarted() override;
  void RenderFrameCreated(content::RenderFrame*) override;