[Mac] Update tab close button when user drags outside

ui/base/cocoa/hover_button.h

Index: ui/base/cocoa/hover_button.h
diff --git a/ui/base/cocoa/hover_button.h b/ui/base/cocoa/hover_button.h
index 1c5923fc0e00aa39afd5e5cc69befc42d4743a8b..b25e29aa3e1d46f64d65829fb9b4972ac7e4ca19 100644
--- a/ui/base/cocoa/hover_button.h
+++ b/ui/base/cocoa/hover_button.h
@@ -27,10 +27,15 @@ UI_BASE_EXPORT
  @private
   // Tracking area for button mouseover states. Nil if not enabled.
   ui::ScopedCrTrackingArea trackingArea_;
+  BOOL mouseDown_;
 }
 
 @property(nonatomic) HoverState hoverState;
 
+// Common initialization called from initWithFrame: and awakeFromNib.
+// Subclassers should call [super commonInit].
+- (void)commonInit;
+
 // Text that would be announced by screen readers.
 - (void)setAccessibilityTitle:(NSString*)accessibilityTitle;