views: mac: Support dynamic resize of title bar height (see #3189)

This is intended for usage with frameless windows that show the standard window
buttons, where resizing the title bar height changes the button offset. Returning a
different value from CefWindowDelegate::GetTitlebarHeight and forcing a resize of
the NSWindow's theme frame (see ViewsWindow::NudgeWindow) will update the
title bar height.

To test:
1. Run `cefclient --use-views --hide-frame --show-window-buttons --url=http://tests/window`
2. Enter a new value for title bar height and click the "Set Titlebar Height" button

tests/cefclient/browser/views_window.h

@@ -130,6 +130,7 @@ class ViewsWindow : public CefBrowserViewDelegate,
 
   bool GetWindowRestorePreferences(cef_show_state_t& show_state,
                                    std::optional<CefRect>& dip_bounds);
+  void SetTitlebarHeight(const std::optional<float>& height);
 
   // CefBrowserViewDelegate methods:
   CefRefPtr<CefBrowserViewDelegate> GetDelegateForPopupBrowserView(
@@ -236,6 +237,8 @@ class ViewsWindow : public CefBrowserViewDelegate,
                               const ImageCache::ImageSet& images);
   void OnExtensionWindowClosed();
 
+  void NudgeWindow();
+
   Delegate* delegate_;  // Not owned by this object.
   CefRefPtr<CefBrowserView> browser_view_;
   bool frameless_;
@@ -258,6 +261,9 @@ class ViewsWindow : public CefBrowserViewDelegate,
 
   CefRefPtr<ViewsOverlayControls> overlay_controls_;
 
+  std::optional<float> default_titlebar_height_;
+  std::optional<float> override_titlebar_height_;
+
   // Structure representing an extension.
   struct ExtensionInfo {
     ExtensionInfo(CefRefPtr<CefExtension> extension, CefRefPtr<CefImage> image)