Improve media-tag export in pad to work with existing CSP

www/common/common-util.js

@@ -207,6 +207,13 @@ define([], function () {
         return Array.prototype.slice.call(A);
     };
 
+    Util.blobToImage = function (blob, cb) {
+        var reader = new FileReader();
+        reader.onloadend = function() {
+            cb(reader.result);
+        };
+        reader.readAsDataURL(blob);
+    };
     Util.blobURLToImage = function (url, cb) {
         var xhr = new XMLHttpRequest();
         xhr.onload = function() {

www/common/cryptpad-common.js

@@ -1498,10 +1498,15 @@ define([
         if (decrypted.callback) {
             var cb = decrypted.callback;
             cb(function (mediaObject) {
-                if (mediaObject.type !== 'download') { return; }
+                var root = mediaObject.element;
-                var root = mediaObject.rootElement;
                 if (!root) { return; }
 
+                if (mediaObject.type === 'image') {
+                    $(root).data('blob', decrypted.blob);
+                }
+
+                if (mediaObject.type !== 'download') { return; }
+
                 var metadata = decrypted.metadata;
 
                 var title = '';

www/pad/inner.js

@@ -477,9 +477,11 @@ define([
         var exportMediaTags = function (inner, cb) {
             var $clone = $(inner).clone();
             nThen(function (waitFor) {
-                $clone.find('media-tag > img').each(function (i, el) {
+                $(inner).find('media-tag').each(function (i, el) {
-                    Util.blobURLToImage($(el).attr('src'), waitFor(function (imgSrc) {
+                    if (!$(el).data('blob')) { return; }
-                        $(el).attr('src', imgSrc);
+                    Util.blobToImage($(el).data('blob'), waitFor(function (imgSrc) {
+                        $clone.find('media-tag[src="' + $(el).attr('src') + '"] img')
+                            .attr('src', imgSrc);
                     }));
                 });
             }).nThen(function () {