js/libs/ember-1.5.1.js
function(callback) {
    var guid = Ember.guidFor(this),
        self = this;

    Ember.$(window).on('popstate.ember-location-'+guid, function(e) {
      // Ignore initial page load popstate event in Chrome
      if (!popstateFired) {
        popstateFired = true;
        if (self.getURL() === self._previousURL) { return; }
      }
      callback(self.getURL());
    });
  }
function(callback) {
    var guid = Ember.guidFor(this),
        self = this;

    Ember.$(window).on('popstate.ember-location-'+guid, function(e) {
      // Ignore initial page load popstate event in Chrome
      if (!popstateFired) {
        popstateFired = true;
        if (self.getURL() === self._previousURL) { return; }
      }
      callback(self.getURL());
    });
  }
Register a callback to be invoked whenever the browser
history changes, including using forward and back buttons.

@private
@method onUpdateURL
@param callback {Function}