Use appendChild instead of innerHTML for security reason

Change-Id: I2d889d4356e3b1e9a72fd4c165cc47a1789b2a64

gr-resemble-diff-mode/gr-resemble-diff-mode.js

diff --git a/gr-resemble-diff-mode/gr-resemble-diff-mode.js b/gr-resemble-diff-mode/gr-resemble-diff-mode.js
index c7b7cba..cd0711a 100644
--- a/gr-resemble-diff-mode/gr-resemble-diff-mode.js
+++ b/gr-resemble-diff-mode/gr-resemble-diff-mode.js
@@ -188,7 +188,7 @@
 
   _handleFullScreen() {
     const w = window.open('about:blank', '_blank');
-    w.document.body.innerHTML = this.$.imageDiff.outerHTML;
+    w.document.body.appendChild(this.$.imageDiff.cloneNode(true));
   }
 }