PubMatic to execute tracker pixel in iframe. (prebid#937)

* PubMatic: passing pageurl in postbid

added support to pass pageURL to PubMatic adapter in postbid (Safeframe) implementation
please note that we have not added safe frame detection logic

* removed code committed accidently in master

* new function createTrackPixelIframeHtml in util

* minor fix in return statement of createTrackPixelIframeHtml

* PubMatic to execute impression tracker in iframe

will use utils.createTrackPixelIframeHtml instead of
utils.createTrackPixelHtml

* utils.createTrackPixelIframeHtml: using string template literals

src/adapters/pubmatic.js

@@ -118,7 +118,7 @@ var PubmaticAdapter = function PubmaticAdapter() {
         adResponse.adSlot = bid.adSlot;
         adResponse.cpm = Number(adUnitInfo.bid);
         adResponse.ad = unescape(adUnit.creative_tag);  // jshint ignore:line
-        adResponse.ad += utils.createTrackPixelHtml(decodeURIComponent(adUnit.tracking_url));
+        adResponse.ad += utils.createTrackPixelIframeHtml(decodeURIComponent(adUnit.tracking_url));
         adResponse.width = dimensions[0];
         adResponse.height = dimensions[1];
         adResponse.dealId = adUnitInfo.wdeal;

src/utils.js

@@ -470,6 +470,19 @@ exports.createTrackPixelHtml = function (url) {
   return img;
 };
 
+/**
+ * Creates a snippet of Iframe HTML that retrieves the specified `url`
+ * @param  {string} url plain URL to be requested
+ * @return {string}     HTML snippet that contains the iframe src = set to `url`
+ */
+exports.createTrackPixelIframeHtml = function (url) {
+  if (!url) {
+    return '';
+  }
+
+  return `<iframe frameborder="0" allowtransparency="true" marginheight="0" marginwidth="0" width="0" hspace="0" vspace="0" height="0" style="height:0p;width:0p;display:none;" scrolling="no" src="${encodeURI(url)}"></iframe>`;
+};
+
 /**
  * Returns iframe document in a browser agnostic way
  * @param  {object} iframe reference