* Electron version: 1.7.3
* Operating system: Windows, MacOS, Linux

### Expected behavior
Context Isolation should work when sandbox option is set to true

### Actual behavior
Context Isolation should work when sandbox option is set to true

### How to reproduce

Turn on contextIsolation and sandbox on browser window. contextIsolation doesn't work. 

contextIsolation work needs to happen on sandbox renderer client as well. 

cc: @tarruda @kevinsawicki @chandrachivukula
atom/renderer/renderer_client_base.h
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;
  virtual bool isolated_world() = 0;
 protected:
  void AddRenderBindings(v8::Isolate* isolate,
                         v8::Local<v8::Object> binding_object);
  
  void RenderThreadStarted() override;
  void RenderFrameCreated(content::RenderFrame*) override;
  void RenderViewCreated(content::RenderView*) override;
  blink::WebSpeechSynthesizer* OverrideSpeechSynthesizer(
      blink::WebSpeechSynthesizerClient* client) override;
  bool OverrideCreatePlugin(content::RenderFrame* render_frame,
                            blink::WebLocalFrame* frame,
                            const blink::WebPluginParams& params,
                            blink::WebPlugin** plugin) override;
  content::BrowserPluginDelegate* CreateBrowserPluginDelegate(
      content::RenderFrame* render_frame,
      const std::string& mime_type,
      const GURL& original_url) override;
  void AddSupportedKeySystems(
      std::vector<std::unique_ptr<::media::KeySystemProperties>>* key_systems)
      override;
 private:
  std::unique_ptr<PreferencesManager> preferences_manager_;
};
}  
#endif