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### Preflight Checklist
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* [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
<!-- Is your feature request related to a problem? Please add a clear and concise description of what the problem is. -->

BrowserWindow currently offers "moved" event related to moving a window, but it only has "will-resize" and "resize" events. I want to save the current dimensions of a window when its size changes, but "will-resize" and "resize" events get fired at every single pixel change. This results in an unnecessarily large number of saving function calls or a need for debouncing the event.

### Proposed Solution
<!-- Describe the solution you'd like in a clear and concise manner -->

Adding "resized" event to BrowserWindow will solve the problem stated above.

### Alternatives Considered
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### Additional Information
<!-- Add any other context about the problem here. -->

shell/browser/native_window.cc
const std::string& item_id,
    const base::DictionaryValue& details) {
  for (NativeWindowObserver& observer : observers_)
    observer.OnTouchBarItemResult(item_id, details);
}
void NativeWindow::NotifyNewWindowForTab() {
  for (NativeWindowObserver& observer : observers_)
    observer.OnNewWindowForTab();
}
void NativeWindow::NotifyWindowSystemContextMenu(int x,
                                                 int y,
                                                 bool* prevent_default) {
  for (NativeWindowObserver& observer : observers_)
    observer.OnSystemContextMenu(x, y, prevent_default);
}
#if defined(OS_WIN)
void NativeWindow::NotifyWindowMessage(UINT message,
                                       WPARAM w_param,
                                       LPARAM l_param) {
  for (NativeWindowObserver& observer : observers_)
    observer.OnWindowMessage(message, w_param, l_param);
}
#endif
views::Widget* NativeWindow::GetWidget() {
  return widget();
}
const views::Widget* NativeWindow::GetWidget() const {