[FIX] web: increase unit test speed

The method removeSrcAttribute is critical, because each changes trigger
this one. this method must be optimized to the maximum to be the fastest.

Before this fix, removeSrcAttribute method search the image and iframe for
all body nodes instead of search only in the inserted nodes, and the method
are very slow.

addons/web/static/tests/helpers/test_utils.js

@@ -314,8 +314,8 @@ function addMockEnvironment(widget, params) {
     });
 
     // make sure images do not trigger a GET on the server
-    $('body').on('DOMNodeInserted.removeSRC', function () {
-        removeSrcAttribute($(this), widget);
+    $('body').on('DOMNodeInserted.removeSRC', function (event) {
+        removeSrcAttribute(event.target, widget);
     });
 
     // make sure the debounce value for input fields is set to 0
@@ -641,27 +641,35 @@ function triggerKeypressEvent(char) {
 /**
  * Removes the src attribute on images and iframes to prevent not found errors,
  * and optionally triggers an rpc with the src url as route on a widget.
+ * This method is critical and must be fastest (=> no jQuery, no underscore)
  *
- * @param {JQueryElement} $el
+ * @param {DOM Node} el
  * @param {[Widget]} widget the widget on which the rpc should be performed
  */
-function removeSrcAttribute($el, widget) {
-    $el.find('img, iframe[src]').each(function () {
-        var $el = $(this);
-        var src = $el.attr('src');
+function removeSrcAttribute(el, widget) {
+    var nodes;
+    if (el.nodeName === 'IMG' || el.nodeName === 'IFRAME') {
+        nodes = [el];
+    } else {
+        nodes = Array.prototype.slice.call(el.getElementsByTagName('img'))
+            .concat(Array.prototype.slice.call(el.getElementsByTagName('iframe')));
+    }
+    var node;
+    while (node = nodes.pop()) {
+        var src = node.attributes.src && node.attributes.src.value;
         if (src && src !== 'about:blank') {
-            if ($el[0].nodeName === 'IMG') {
-                $el.attr('data-src', src);
-                $el.removeAttr('src');
+            var $el = $(node);
+            node.setAttribute('data-src', src);
+            if (node.nodeName === 'IMG') {
+                node.attributes.removeNamedItem('src');
             } else {
-                $el.attr('data-src', src);
-                $el.attr('src', 'about:blank');
+                node.setAttribute('src', 'about:blank');
             }
             if (widget) {
                 widget._rpc({route: src});
             }
         }
-    });
+    }
 }
 
 var patches = {};