function getEventModifiers(e) {
    var modifiers = 0;
    if (e.ctrlKey) {
      modifiers |= wtf.ui.ModifierKey.CTRL;
    }
    if (e.altKey) {
      modifiers |= wtf.ui.ModifierKey.ALT;
    }
    if (e.shiftKey) {
      modifiers |= wtf.ui.ModifierKey.SHIFT;
    }
    if (e.meltaKey) {
      modifiers |= wtf.ui.ModifierKey.META;
    }
    return modifiers;
  }
Toggles input events on the control root, dispatching tooltip and paint
events.
@param {boolean} value True to enable events.
@private