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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
options.Get(options::kUseContentSize, &use_content_size);
  
  extensions::SizeConstraints size_constraints(
      use_content_size ? GetContentSizeConstraints() : GetSizeConstraints());
  int min_height = 0, min_width = 0;
  if (options.Get(options::kMinHeight, &min_height) |
      options.Get(options::kMinWidth, &min_width)) {
    size_constraints.set_minimum_size(gfx::Size(min_width, min_height));
  }
  int max_height = INT_MAX, max_width = INT_MAX;
  if (options.Get(options::kMaxHeight, &max_height) |
      options.Get(options::kMaxWidth, &max_width)) {
    size_constraints.set_maximum_size(gfx::Size(max_width, max_height));
  }
  if (use_content_size) {
    SetContentSizeConstraints(size_constraints);
  } else {
    SetSizeConstraints(size_constraints);
  }
#if defined(OS_WIN) || defined(OS_LINUX)
  bool resizable;
  if (options.Get(options::kResizable, &resizable)) {
    SetResizable(resizable);
  }
  bool closable;
  if (options.Get(options::kClosable, &closable)) {
    SetClosable(closable);
  }
#endif
  bool movable;