New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  minLat: 42.257645,
  minLng: -71.808530,
  maxLat: 42.265083,
  maxLng: -71.794659,

  bounds: function() {
    var minLat = parseFloat(this.get('minLat').toFixed(6));
    var minLng = parseFloat(this.get('minLng').toFixed(6));
    var maxLat = parseFloat(this.get('maxLat').toFixed(6));
    var maxLng = parseFloat(this.get('maxLng').toFixed(6));

    return L.latLngBounds([[minLat, minLng],
      [maxLat, maxLng]]);

  }.property('minLat,minLng,maxLat,maxLng'),

  actions: {
    updateMax(r,e) {
      var location = e.target.getLatLng();
      this.set('maxLat', location.lat);
      this.set('maxLng', location.lng);
    },
    updateMin(r,e) {
      var location = e.target.getLatLng();
      this.set('minLat', location.lat);
      this.set('minLng', location.lng);
    } 
  }
});

styles.app.css

html, body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
  height: 100%;
  width: 100%;
}

.leaflet-container {
  height: 600px;
}

templates.application.hbs

{{#leaflet-map bounds=bounds}}
  {{tile-layer url="http://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png"}}
 
  {{marker-layer lat=minLat lng=minLng draggable=true onDragend=(action "updateMin" r)}}
  {{marker-layer lat=maxLat lng=maxLng draggable=true onDragend=(action "updateMax" r)}}
{{/leaflet-map}}

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0",
    	"leaflet": "~0.7.7"
  },
  "addons": {
   "ember-leaflet": "2.2.7"
 
  }
}