instanceof check breaks mapbox-gl-js in multiframe environment

Nobody has claimed this yet.

**mapbox-gl-js version**: 0.53.0

**browser**: chrome / safari

**culprit**: [map.js](https://github.com/mapbox/mapbox-gl-js/blob/master/src/ui/map.js#L346)

### Steps to Trigger Behavior
render mapbox inside new environment (eg. window.open)
1). create a popup (window.open)
2). use React.createPortal to render the map component
3). Render map inside component

### Link to Demonstration
https://codesandbox.io/s/qllpz89w39

### Expected Behavior
code doesnt throw an error because container check fails while container is actually of the correct type (HTMLElement)

### Actual Behavior
code throws an error because instanceof fails within different environments

more informatiion in this article:
[instanceof considered harmful](http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/)

Start at src/ui/map.js#L346 and reproduce the failure using the linked CodeSandbox with a map rendered in a window.open environment through React.createPortal. Verify the container check accepts the correct HTMLElement across browsing contexts without throwing, while preserving normal container validation.

Written by the indexing model from the issue text.