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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/renderer_client_base.h
#ifndef ATOM_RENDERER_RENDERER_CLIENT_BASE_H_
#define ATOM_RENDERER_RENDERER_CLIENT_BASE_H_
#include <memory>
#include <string>
#include <vector>
#include "content/public/renderer/content_renderer_client.h"
#include "third_party/blink/public/web/web_local_frame.h"
#include "widevine_cdm_version.h"  
#if defined(WIDEVINE_CDM_AVAILABLE)
#include "chrome/renderer/media/chrome_key_systems_provider.h"
#endif
namespace atom {
class PreferencesManager;
class RendererClientBase : public content::ContentRendererClient {
 public:
  RendererClientBase();
  ~RendererClientBase() override;
  virtual void DidCreateScriptContext(v8::Handle<v8::Context> context,
                                      content::RenderFrame* render_frame);
  virtual void WillReleaseScriptContext(v8::Handle<v8::Context> context,
                                        content::RenderFrame* render_frame) = 0;
  virtual void DidClearWindowObject(content::RenderFrame* render_frame);
  virtual void SetupMainWorldOverrides(v8::Handle<v8::Context> context) = 0;
  bool isolated_world() const { return isolated_world_; }
  
  v8::Local<v8::Context> GetContext(blink::WebLocalFrame* frame,
                                    v8::Isolate* isolate) const;
  
  static v8::Local<v8::Value> RunScript(v8::Local<v8::Context> context,