Fixes issue that doesn't let api set labels

Introduced in a499e3d9382fef139294472f4853d0d8f7e76931. The
setLabelValue function in the reply dialog was not updated to correspond
with the change breaking gr-label-scores out into a separate element.
This change updates the function to work and also adds a unit test.

Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=719927
Bug: https://bugs.chromium.org/p/gerrit/issues/detail?id=5757
Change-Id: I4727e3f631ce14526f01c3cb9291cbf917c5cfac
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 0bb548b..60d3c4f 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
@@ -177,7 +177,8 @@
     },
 
     setLabelValue: function(label, value) {
-      var selectorEl = this.$$('iron-selector[data-label="' + label + '"]');
+      var selectorEl =
+          this.$.labelScores.$$('iron-selector[data-label="' + label + '"]');
       // The selector may not be present if it’s not at the latest patch set.
       if (!selectorEl) { return; }
       var item = selectorEl.$$('gr-button[data-value="' + value + '"]');
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
index 253f01c..34ac167 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
@@ -214,6 +214,17 @@
       });
     });
 
+    test('setlabelValue', function() {
+      element._account = {_account_id: 1};
+      flushAsynchronousOperations();
+      var label = 'Verified';
+      var value = '+1';
+      element.setLabelValue(label, value);
+      flushAsynchronousOperations();
+      var labels = element.$.labelScores.getLabelValues();
+      assert.deepEqual(labels, {'Verified': 1});
+    });
+
     function getActiveElement() {
       return Polymer.IronOverlayManager.deepActiveElement;
     }