long-tap context menu event on mobile chrome delayed by a click

Nobody has claimed this yet.

**v0.32.1**:

### Steps to Trigger Behavior

1. Open [jsfiddle](https://jsfiddle.net/7Lfwbkpb/2/) (on Chrome 56.0.2924.87)
2. This only reproduces itself on a mobile browser, so launch the dev tools (Ctrl-Shift-i or right-click->Inspect)
3. Pick a mobile device (I use Nexus 5):

### Expected Behavior
long tap on map should trigger the alter dialog registered on "contextmenu" event.

### Actual Behavior
long tap and subsequent tap trigger the dialog.

### Motivation
I am trying to reconcile the event handling among browsers and of course they all behave differently.
so far my code registered on long taps manually:

`

"mousedown" : function(e) {
clearTimeout(triggerTimout);
triggerTimout = setTimeout(function() {
e.latlng = e.lngLat;
cb(e);
}, 1000);
},
"mousemove" : function(e) { clearTimeout(triggerTimout); },
"mouseup" : function(e) {
clearTimeout(triggerTimout);
}
`

but that doesn't work on FF (does on Safari and Chrome) - FF never relays "mousedown" events if they part of a long-tap.
changing to touch events hampers my dev enviroment;
"contextmenu" works well on FF, but not on chrome.

This is of course quite nighmare-ish - but mapboxgl [does issue](https://github.com/mapbox/mapbox-gl-js/blob/b9e10b939c6a3fe5d7ecac209f751b4871970ede/src/ui/bind_handlers.js#L54) "contextmenu" events and it doesn't look like it does this correctly in the circumstances described.

Start with the contextmenu handling in src/ui/bind_handlers.js, then reproduce the jsfiddle case using Chrome mobile emulation and the reported Nexus 5 profile. Compare long-tap behavior with the expected immediate dialog and the delayed click-triggered dialog; done means the event behavior is reconciled without breaking the Firefox and Safari cases described.

Written by the indexing model from the issue text.