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/window_test_runner.h

@@ -8,6 +8,8 @@
 
 #include "include/cef_browser.h"
 
+#include <optional>
+
 namespace client {
 namespace window_test {
 
@@ -15,6 +17,8 @@ namespace window_test {
 // the browser process UI thread unless otherwise indicated.
 class WindowTestRunner {
  public:
+  virtual ~WindowTestRunner() = default;
+
   virtual void SetPos(CefRefPtr<CefBrowser> browser,
                       int x,
                       int y,
@@ -28,7 +32,8 @@ class WindowTestRunner {
   // corner of the display.
   static void ModifyBounds(const CefRect& display, CefRect& window);
 
-  virtual ~WindowTestRunner() {}
+  virtual void SetTitleBarHeight(CefRefPtr<CefBrowser> browser,
+                                 const std::optional<float>& height);
 };
 
 }  // namespace window_test