function isFallbackCompositionEnd(topLevelType, nativeEvent) {
	  switch (topLevelType) {
	    case 'topKeyUp':
	      // Command keys insert or clear IME input.
	      return END_KEYCODES.indexOf(nativeEvent.keyCode) !== -1;
	    case 'topKeyDown':
	      // Expect IME keyCode on each keydown. If we get any other
	      // code we must have exited earlier.
	      return nativeEvent.keyCode !== START_KEYCODE;
	    case 'topKeyPress':
	    case 'topMouseDown':
	    case 'topBlur':
	      // Events are not possible without cancelling IME.
	      return true;
	    default:
	      return false;
	  }
	}
Does our fallback mode think that this event is the end of composition?

@param {string} topLevelType
@param {object} nativeEvent
@return {boolean}