Bug 1633362 - Add a use counter for Document.mozSetImageElement. r=smaug

It complicates all the ID tracking code and the SVG code quite a bit.

I want to know if it is used so that we can maybe remove it.

Differential Revision: https://phabricator.services.mozilla.com/D72613

dom/base/UseCounters.conf

@@ -134,6 +134,9 @@ custom MozGetUserMediaXOrigin calls Navigator.mozGetUserMedia from a cross origi
 method MediaDevices.getDisplayMedia
 custom GetDisplayMediaXOrigin calls MediaDevices.getDisplayMedia from a cross origin context
 
+// Non-standard Document.mozSetImageElement.
+method Document.mozSetImageElement
+
 // Missing-property use counters.  We claim these are "method" use
 // counters, because we don't need a separate description string for
 // them and we only need one use counter, not a getter/setter pair.

dom/webidl/Document.webidl

@@ -241,6 +241,7 @@ partial interface Document {
    *
    * @see <https://developer.mozilla.org/en/DOM/document.mozSetImageElement>
    */
+  [UseCounter]
   void mozSetImageElement(DOMString aImageElementId,
                           Element? aImageElement);