Fix the ReviewInput format for attention set changes

Change-Id: I9671b1352162fc58e658fb6df30dd17dfb169d42
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.js b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.js
index f3c31aa..24bc142 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.js
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.js
@@ -546,13 +546,19 @@
       reviewInput.add_to_attention_set = [];
       for (const user of this._newAttentionSet) {
         if (!this._currentAttentionSet.has(user)) {
-          reviewInput.add_to_attention_set.push(user);
+          reviewInput.add_to_attention_set.push({
+            user,
+            reason: 'manually added in reply dialog',
+          });
         }
       }
       reviewInput.remove_from_attention_set = [];
       for (const user of this._currentAttentionSet) {
         if (!this._newAttentionSet.has(user)) {
-          reviewInput.remove_from_attention_set.push(user);
+          reviewInput.remove_from_attention_set.push({
+            user,
+            reason: 'manually removed in reply dialog',
+          });
         }
       }
     }
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
index 4c65298..456adb5 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
@@ -181,13 +181,17 @@
   });
 
   test('modified attention set', done => {
+    element._newAttentionSet = new Set([314]);
     const buttonEl = element.shadowRoot.querySelector('.edit-attention-button');
     MockInteractions.tap(buttonEl);
     flushAsynchronousOperations();
 
     stubSaveReview(review => {
       assert.isTrue(review.ignore_default_attention_set_rules);
-      assert.deepEqual(review.add_to_attention_set, []);
+      assert.deepEqual(review.add_to_attention_set, [{
+        user: 314,
+        reason: 'manually added in reply dialog',
+      }]);
       assert.deepEqual(review.remove_from_attention_set, []);
       done();
     });