Merge "Clean up nodes observer before adding new ones for gr-diff"

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js

diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
index 58a5b65..189d0f1 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
@@ -856,6 +856,7 @@
   }
 
   _handleRenderContent() {
+    this._unobserveIncrementalNodes();
     this._incrementalNodeObserver = dom(this).observeNodes(info => {
       const addedThreadEls = info.addedNodes.filter(isThreadEl);
       // Removed nodes do not need to be handled because all this code does is