[SalesForce] the equivalent of a Visualforce page in Lightning Experience

I have found the following to work in my VF pages when transitioning to LEX:

(function(myContext){
    myContext.ForceUI = myContext.ForceUI || {};

    myContext.ForceUI.isSalesforce1 = function() {
        return((typeof sforce != 'undefined') && sforce && (!!sforce.one));
    }
})(this);

Then you can use (as an example):

ForceUI.isSalesforce1() ? navigateToSObject(aId) : (window.location.href='/' + aId);

https://developer.salesforce.com/docs/atlas.en-us.salesforce1.meta/salesforce1/vf_dev_best_practices_pages_multipurpose.htm

Also, see my answer here for a template to use to navigate as needed and make it easy to transition your VF pages:

What is suggested approach to transfer VF pages to be lightning ready

In the end it was sufficient for us to assume that the screen was being launched from the List View. If we need variations then I think we'll try to make a VF component and wrap that with different pages for different contexts. We'll cross that bridge when we come to it.

For now we have the following on the VF controller:

public String getReferer(){
    Id filterId = setController.getFilterId();
    String baseUrl = ApexPages.currentPage().getHeaders().get('Referer');
    String fullUrl = baseUrl + 'one/one.app#/sObject/Contact/list?filterName=' + filterId;
    return fullUrl;
}

In the VF we then pass a handler into the component when we construct it:

closePopoverHandler = function( event )  {
                                            window.top.location = '{!referer}' ;
                                         };


$Lightning.use( "c:OurLightningApp", function() {
      $Lightning.createComponent( "c:OurLightningComponent",
                                  { param1: 'value1' },
                                  "DivToReplace",
                                  function(cmp) {
                                          $A.eventService.addHandler({
                                               event: 'force:closeQuickAction',
                                               handler: closePopoverHandler
                                           });
                                   });
                               });

And then ensure that the LightningApp has the following dependancy:

<aura:dependency resource="markup://force:*" type="EVENT"/>

That said, as an alternative for finding the URL to return to - a more generic solution would be to use the ApexPages parameters, which sometimes contains the return url.

String retUrl = ApexPages.currentPage().getParameters().get('vfRetURLInSFX' );
if ( String.isNotEmpty( retUrl ) ) {
    //
    // the retUrl is in the parameters, so we should just return it
    //
    return retUrl;
}
//
// We can assume have been launched from a related list on an object, and so the url has to be constructed
//
String baseUrl = ApexPages.currentPage().getHeaders().get('Referer');
return baseUrl + 'one/one.app#/sObject/' + apexpages.currentpage().getparameters().get('id');