### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

### Problem Description
When working with BrowserViews, there's no way to listen to focus changes on either BrowserView itself or its WebContents.

### Proposed Solution
On BrowserWindow, there are `focus` and `blur` events. The same events need to be emitted on BrowserView/WebContents.
i.e. : 
```
browserView.on('focus', () => {
    // view is focused, do stuff
});
```
or  
```
browserView.webContents.on('focus', () => {
    // contents are focused, do stuff
});
```

### Alternatives Considered
I can't think of a good way of working around this lack of functionality
shell/browser/api/electron_api_web_contents.cc
} else {
    settings.SetBoolKey(printing::kSettingHeaderFooterEnabled, false);
  }
   We don't want to allow the user to enable these settings
   but we need to set them or a CHECK is hit.
  settings.SetIntKey(printing::kSettingPrinterType,
                     static_cast<int>(printing::mojom::PrinterType::kLocal));
  settings.SetBoolKey(printing::kSettingShouldPrintSelectionOnly, false);
  settings.SetBoolKey(printing::kSettingRasterizePdf, false);
   Set custom page ranges to print
  std::vector<gin_helper::Dictionary> page_ranges;
  if (options.Get("pageRanges", &page_ranges)) {
    base::Value page_range_list(base::Value::Type::LIST);
    for (auto& range : page_ranges) {
      int from, to;
      if (range.Get("from", &from) && range.Get("to", &to)) {
        base::Value range(base::Value::Type::DICTIONARY);
         Chromium uses 1-based page ranges, so increment each by 1.
        range.SetIntKey(printing::kSettingPageRangeFrom, from + 1);
        range.SetIntKey(printing::kSettingPageRangeTo, to + 1);
        page_range_list.Append(std::move(range));
      } else {
        continue;
      }
    }
    if (!page_range_list.GetList().empty())
      settings.SetPath(printing::kSettingPageRange, std::move(page_range_list));
  }
   Duplex type user wants to use.
  printing::mojom::DuplexMode duplex_mode =