Make gr-change-list a true HTML table

- Remove all flex attributes from from change list CSS (with the
  exception of mobile).
  - Add flex properties for change list items with media queries.
- <tr> wrapped around gr-change-list-item doesn't work in the table.
  Instead, style <gr-change-list-item> to be display: table-row.

Bug: Issue 5285
Change-Id: I576ddbda3c1697c3476620a5e8ea9db727e08557
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item.html b/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item.html
index 202b1dd..0df017b 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item.html
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item.html
@@ -26,7 +26,7 @@
   <template>
     <style>
       :host {
-        display: flex;
+        display: table-row;
         border-bottom: 1px solid #eee;
       }
       :host([selected]) {
@@ -42,7 +42,6 @@
         background-color: #fcfaa6;
       }
       .cell {
-        flex-shrink: 0;
         padding: .3em .5em;
       }
       a {
@@ -71,6 +70,11 @@
       .u-gray-background {
         background-color: #F5F5F5;
       }
+      @media only screen and (max-width: 50em) {
+        :host {
+          display: flex;
+        }
+      }
     </style>
     <style include="gr-change-list-styles"></style>
     <td class="cell keyboard">