Fix bug where changeURL was not updating to reflect its change object

Computed bindings are recomputed (say, on a model update), when the
arguments to the computation function change. Since no arguments were
being passed to changeURL(), it was only being computed once.

In order to maintain a clean API for external callers, move changeURL
from a function to a computed property. This way the caller doesn't
have to pass in the change number but it still updates when the change
number does.

Bug: Issue 3689
Change-Id: I92a659b3c917f77d4e212c98af7c763174756074

polygerrit-ui/app/elements/gr-change-list-item.html

@@ -76,7 +76,7 @@ limitations under the License.
         <span class="positionIndicator">&#x25b6;</span>
       </td>
       <td>
-        <a href$="[[changeURL()]]">[[change.subject]]</a>
+        <a href$="[[changeURL]]">[[change.subject]]</a>
       </td>
       <td>[[_computeChangeStatusString(change)]]</td>
       <td>
@@ -118,11 +118,15 @@ limitations under the License.
           reflectToAttribute: true,
         },
         change: Object,
+        changeURL: {
+          type: String,
+          computed: '_computeChangeURL(change._number)',
+        }
       },
 
-      changeURL: function() {
-        if (!this.change) { return ''; }
-        return '/c/' + this.change._number + '/';
+      _computeChangeURL: function(changeNum) {
+        if (!changeNum) { return ''; }
+        return '/c/' + changeNum + '/';
       },
 
       _computeChangeStatusString: function(change) {

polygerrit-ui/app/elements/gr-change-list.html

@@ -111,7 +111,7 @@ limitations under the License.
       _changeURLForIndex: function(index) {
         var changeEls = this._getNonHeaderListItems();
         if (index < changeEls.length && changeEls[index]) {
-          return changeEls[index].changeURL();
+          return changeEls[index].changeURL;
         }
         return '';
       },

polygerrit-ui/app/test/gr-change-list-item-test.html

@@ -82,7 +82,9 @@ limitations under the License.
           '/q/status:open+project:combustible-stuff+branch:lemons');
 
       element.change = { _number: 42 };
-      assert.equal(element.changeURL(), '/c/42/');
+      assert.equal(element.changeURL, '/c/42/');
+      element.change = { _number: 43 };
+      assert.equal(element.changeURL, '/c/43/');
     });
 
   });