[MacViews] Enable dragging a window by its caption/draggable areas.

ui/views/cocoa/cocoa_non_client_drag.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_COCOA_COCOA_NON_CLIENT_DRAG_H_
+#define UI_VIEWS_COCOA_COCOA_NON_CLIENT_DRAG_H_
+
+#include "base/macros.h"
+#import "ui/views/cocoa/native_widget_mac_nswindow.h"
+#include "ui/views/views_export.h"
+
+@interface CocoaNonClientDragMaskView : NSView
+@end
+
+@interface NativeWidgetMacNSWindow (CocoaNonClientDrag)
+// Called when the application receives a mouse-down, but before the event
+// is processed by NSWindows. Returns NO if the event should be processed as-is,
+// or YES if the event should be reposted to handle window dragging. Events are
+// reposted at the CGSessionEventTap level because window dragging happens there
+// before the application receives the event.
+- (BOOL)willReceiveLeftMouseDown:(NSPoint)locationInWindow;
+@end
+
+namespace views {
+
+// Support window caption/draggable regions.
+// In AppKit, non-client regions are set by overriding
+// -[NSView mouseDownCanMoveWindow]. NSApplication caches this area as views are
+// installed and performs window moving when mouse-downs land in the area.
+// In Views, non-client regions are determined via hit-tests when the event
+// occurs.
+// To bridge the two models, we monitor mouse-downs with
+// +[NSEvent addLocalMonitorForEventsMatchingMask:handler:]. This receives
+// events after window dragging is handled, so for mouse-downs that land on a
+// draggable point, we cancel the event and repost it at the CGSessionEventTap
+// level so that window dragging will be handled again.
+class VIEWS_EXPORT CocoaNonClientDrag {
+ public:
+  CocoaNonClientDrag();
+  ~CocoaNonClientDrag();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CocoaNonClientDrag);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_COCOA_COCOA_NON_CLIENT_DRAG_H_