FLUID-5872: Added a comment and refactored src setting

Moved the setting of the iframe source to after the binding of the "load" listener
to ensure that the load event isn't triggered before binding to the event.

tests/component-tests/tooltip/js/TooltipTests.js

@@ -212,7 +212,6 @@ https://github.com/fluid-project/infusion/raw/master/Infusion-LICENSE.txt
     });
 
     fluid.tests.tooltip.FLUID5846.setupIframe = function (that, iframeSrc, iframe) {
-        $(iframe).attr("src", iframeSrc);
         $(iframe).load(function () {
             // DO NOT MOVE this property access outside this function!
             var dokkument = iframe.contentDocument;
@@ -221,6 +220,11 @@ https://github.com/fluid-project/infusion/raw/master/Infusion-LICENSE.txt
             that.iframeBody = iframejQuery("body", dokkument);
             that.events.iframeReady.fire();
         });
+
+        // Programmatically setting the iframe src to ensure that the load event
+        // is triggered after we have bound our listener.
+        // see: https://issues.fluidproject.org/browse/FLUID-5872
+        $(iframe).attr("src", iframeSrc);
     };
 
     fluid.defaults("fluid.tests.tooltip.FLUID5846.parent", {