code: function removeGlobalKeydownHook(hook) {
          var index = _globalKeydownHooks.indexOf(hook);
          if (index !== -1) {
              _globalKeydownHooks.splice(index, 1);
          }
      }
docs: Removes a global keydown hook added by `addGlobalKeydownHook`.
  Does not need to be the most recently added hook.
  
  @param {function(Event): boolean} hook The global hook to remove.