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### Issue Details

* **Electron Version:**
  * 10.1.3
* **Operating System:**
  * win7 sp1 x64

- without worldSafeExecuteJavaScript, `(webFrame|webContents).executeJavaScript('new Promise(resolve => setTimeout(() => resolve(2), 3000));')` works as expected; the executeJavaScript promise waits for the eval promise.
- in the case of webFrame the evaled promise is returned raw
- in the case of webContents the promise is marshaled
- with worldSafeExecuteJavaScript, both error with: "An object could not be cloned"
- webContents should continue marshaling promises, otherwise its an unnecessary breaking change
- webFrame should marshal promises for consistency with webContents
- the clone restriction would be on the promise resolve value

### To Reproduce
`(webFrame|webContents).executeJavaScript('new Promise(resolve => setTimeout(() => resolve(2), 3000));')`


shell/renderer/api/electron_api_web_frame.cc
public:
  FrameSetSpellChecker(SpellCheckClient* spell_check_client,
                       content::RenderFrame* main_frame)
      : spell_check_client_(spell_check_client), main_frame_(main_frame) {
    content::RenderFrame::ForEach(this);
    main_frame->GetWebFrame()->SetSpellCheckPanelHostClient(spell_check_client);
  }
  bool Visit(content::RenderFrame* render_frame) override {
    auto* view = render_frame->GetRenderView();
    if (view->GetMainRenderFrame() == main_frame_ ||
        (render_frame->IsMainFrame() && render_frame == main_frame_)) {
      render_frame->GetWebFrame()->SetTextCheckClient(spell_check_client_);
    }
    return true;
  }
 private:
  SpellCheckClient* spell_check_client_;
  content::RenderFrame* main_frame_;
  DISALLOW_COPY_AND_ASSIGN(FrameSetSpellChecker);
};
class SpellCheckerHolder final : public content::RenderFrameObserver {