Hide reviewed checkbox when edit is loaded

Modifying the reviewed state of an edit patchset is an illogical action,
and should be disabled.

This change utilizes the _editLoaded property of gr-change-view to
conditionally hide the reviewed checkbox from the file list. In
addition, attempts to modify the reviewed state (e.g. with a hotkey)
are treated as a no-op, and the user is shown a toast.

TODO: Further utilize this approach to conditionally show buttons for
modifying an edit patchset. Will be done in a later change.

Bug: Issue 4437
Change-Id: Iee33d7ebbe0a7182cb91ca6168813154775d9ab4

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

@@ -1267,7 +1267,30 @@ limitations under the License.
       element._handleEscKey(mockEvent);
       assert.isFalse(element._displayLine);
     });
-  });
 
+    suite('editLoaded behavior', () => {
+      const isVisible = el => {
+        assert.ok(el);
+        return getComputedStyle(el).getPropertyValue('display') !== 'none';
+      };
+
+      test('reviewed checkbox', () => {
+        const alertStub = sandbox.stub();
+        element.addEventListener('show-alert', alertStub);
+        element.editLoaded = false;
+        // Reviewed checkbox should be shown.
+        assert.isTrue(isVisible(element.$$('.reviewed')));
+        MockInteractions.pressAndReleaseKeyOn(element, 82, null, 'r');
+        assert.isFalse(alertStub.called);
+
+        element.editLoaded = true;
+        flushAsynchronousOperations();
+
+        assert.isFalse(isVisible(element.$$('.reviewed')));
+        MockInteractions.pressAndReleaseKeyOn(element, 82, null, 'r');
+        assert.isTrue(alertStub.called);
+      });
+    });
+  });
   a11ySuite('basic');
 </script>