fix: move window buttons in-place on macOS (#30322)

shell/browser/ui/cocoa/window_buttons_proxy.h

@@ -0,0 +1,66 @@
+// Copyright (c) 2021 Microsoft, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_BROWSER_UI_COCOA_WINDOW_BUTTONS_PROXY_H_
+#define SHELL_BROWSER_UI_COCOA_WINDOW_BUTTONS_PROXY_H_
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/mac/scoped_nsobject.h"
+#include "third_party/abseil-cpp/absl/types/optional.h"
+#include "ui/gfx/geometry/point.h"
+
+@class WindowButtonsProxy;
+
+// A helper view that floats above the window buttons.
+@interface ButtonsAreaHoverView : NSView {
+ @private
+  WindowButtonsProxy* proxy_;
+}
+- (id)initWithProxy:(WindowButtonsProxy*)proxy;
+@end
+
+// Manipulating the window buttons.
+@interface WindowButtonsProxy : NSObject {
+ @private
+  NSWindow* window_;
+  // The view that contains the window buttons and title.
+  NSView* titlebar_container_;
+
+  // The window buttons.
+  NSButton* left_;
+  NSButton* right_;
+  NSButton* middle_;
+
+  // Current left-top margin of buttons.
+  gfx::Point margin_;
+  // The default left-top margin.
+  gfx::Point default_margin_;
+
+  // Track mouse moves above window buttons.
+  BOOL show_on_hover_;
+  BOOL mouse_inside_;
+  base::scoped_nsobject<NSTrackingArea> tracking_area_;
+  base::scoped_nsobject<ButtonsAreaHoverView> hover_view_;
+}
+
+- (id)initWithWindow:(NSWindow*)window;
+
+- (void)setVisible:(BOOL)visible;
+- (BOOL)isVisible;
+
+// Only show window buttons when mouse moves above them.
+- (void)setShowOnHover:(BOOL)yes;
+
+// Set left-top margin of the window buttons..
+- (void)setMargin:(const absl::optional<gfx::Point>&)margin;
+
+// Return the bounds of all 3 buttons, with margin on all sides.
+- (NSRect)getButtonsContainerBounds;
+
+- (void)redraw;
+- (void)updateTrackingAreas;
+@end
+
+#endif  // SHELL_BROWSER_UI_COCOA_WINDOW_BUTTONS_PROXY_H_