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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/browser/web_contents_preferences.cc
std::string* value) const {
  return GetAsString(&preference_, name, value);
}
bool WebContentsPreferences::GetPreloadPath(base::FilePath* path) const {
  DCHECK(path);
  base::FilePath::StringType preload_path;
  if (GetAsString(&preference_, options::kPreloadScript, &preload_path)) {
    base::FilePath preload(preload_path);
    if (preload.IsAbsolute()) {
      *path = std::move(preload);
      return true;
    } else {
      LOG(ERROR) << "preload script must have absolute path.";
    }
  } else if (GetAsString(&preference_, options::kPreloadURL, &preload_path)) {
    
    base::FilePath preload;
    if (net::FileURLToFilePath(GURL(preload_path), &preload)) {
      *path = std::move(preload);
      return true;
    } else {
      LOG(ERROR) << "preload url must be file:// protocol.";
    }
  }
  return false;
}
content::WebContents* WebContentsPreferences::GetWebContentsFromProcessID(