Update reply counter when adding drafts to inline diffs

Also do a small cleanup of _boundScrollHandler in favor of
Polymer.{listen|unlisten}

Bug: Issue 4119
Change-Id: I16e0f74dd3f480f99b837cdf6664603a94dcc06f
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
index ded5108..646dfde 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
@@ -35,6 +35,12 @@
      * @event comment-discard
      */
 
+    /**
+     * Fired when this comment is saved.
+     *
+     * @event comment-save
+     */
+
     properties: {
       changeNum: String,
       comment: {
@@ -86,6 +92,7 @@
           }
           this.comment = comment;
           this.editing = false;
+          this.fire('comment-save');
 
           return obj;
         }.bind(this));