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diff --git a/widget/cocoa/MOZMenuOpeningCoordinator.h b/widget/cocoa/MOZMenuOpeningCoordinator.h
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+++ b/widget/cocoa/MOZMenuOpeningCoordinator.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZMenuOpeningCoordinator_h
+#define MOZMenuOpeningCoordinator_h
+
+#import <Cocoa/Cocoa.h>
+
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+class Runnable;
+}
+
+/*
+ * MOZMenuOpeningCoordinator is a workaround for the fact that opening an NSMenu
+ * creates a nested event loop. This event loop is only exited after the menu is
+ * closed. The caller of NativeMenuMac::ShowAsContextMenu does not expect
+ * ShowAsContextMenu to create a nested event loop, so we need to make sure to
+ * open the NSMenu asynchronously.
+ */
+
+@interface MOZMenuOpeningCoordinator : NSObject
+
++ (instancetype)sharedInstance;
+
+// Queue aMenu for opening.
+// The menu will open from a new event loop tick so that its nested event loop
+// does not block the caller. If another menu's nested event loop is currently
+// on the stack, we wait for that nested event loop to unwind before opening
+// aMenu. Returns a handle that can be passed to cancelAsynchronousOpening:. Can
+// only be called on the main thread.
+- (NSInteger)asynchronouslyOpenMenu:(NSMenu*)aMenu
+                   atScreenPosition:(NSPoint)aPosition
+                            forView:(NSView*)aView
+                     withAppearance:(NSAppearance*)aAppearance
+                      asContextMenu:(BOOL)aIsContextMenu;
+
+// If the menu opening request for aHandle hasn't been processed yet, cancel it.
+// Can only be called on the main thread.
+- (void)cancelAsynchronousOpening:(NSInteger)aHandle;
+
+// This field is a terrible workaround for a gnarly problem.
+// It should be set to YES by the caller of -[NSMenu
+// cancelTracking(WithoutAnimation)]. This field gets checked by the native
+// event loop code in nsAppShell.mm to avoid calling
+// -[NSApplication nextEventMatchingMask:...] between the call to cancelTracking
+// and the point at which the menu has finished closing and unwound from its
+// tracking event loop, because such calls can interfere with menu closing and
+// get us stuck in the menu event loop forever.
+@property(class) BOOL needToUnwindForMenuClosing;
+
+@end
+
+#endif  // MOZMenuOpeningCoordinator_h