src/vs/editor/common/viewModelEventDispatcher.ts/ViewModelEventDispatcher/addViewEventHandler
class ViewModelEventDispatcher:	public addViewEventHandler(eventHandler: ViewEventHandler): void {
		for (let i = 0, len = this._eventHandlers.length; i < len; i++) {
			if (this._eventHandlers[i] === eventHandler) {
				console.warn('Detected duplicate listener in ViewEventDispatcher', eventHandler);
			}
		}
		this._eventHandlers.push(eventHandler);
	}