EventListener return value is ignored in html bindings

[DartBot]

This issue was originally filed by danrice...@gmail.com

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I am trying to intercept the right-click context menu as follows:

Window _window;
_window.on.contextMenu.add((Event event) {return false; });

This code is in fact called when I click the right mouse button in the browser window, but the 'return false' no longer has the desired effect of preventing the browser context menu from appearing, as it did in the previous DOM bindings.

A cursory inspection of the DOM code shows that contextMenu is a getter on the WindowEvents interface, returning an EventListenerList, and EventListenerList.add takes an EventListener as its first argument. However, EventListener is defined as a void function, while the standard DOM allows a return value in order to provide a way to cancel the event.

[DartBot]

This comment was originally written by rice@google.com

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Added Invalid label.