Pass change to <gr-message>

The change object is ultimately needed further down in the DOM tree in
<gr-linked-text>. That is how the project wide configured comment links
are handed down. Not a great way of state management, but that is how it
is at the moment. So let's be happy about this simple fix.

Bug: Issue 12880
Change-Id: I4f06de7b09e2ec8b6fc7361d76bfdba29be3c984
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
index 5fd64d2..56cb960 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
@@ -111,6 +111,7 @@
     filter="_isMessageVisible"
   >
     <gr-message
+      change="[[change]]"
       change-num="[[changeNum]]"
       message="[[message]]"
       project-name="[[projectName]]"