ChangeScreen2: Hide expand/collapse arrow on short messages

ChangeScreen2 was supposed to call onShowView() to hide the
expand/collapse arrow on short commit messages, and ensure
it is visible on longer ones. This call was somehow dropped
during ae561aec17.

Change-Id: Ie938b343e00326f8aaf78a044d7aacae56b14502

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/ChangeScreen2.java

@@ -340,7 +340,7 @@ public class ChangeScreen2 extends Screen {
   @Override
   public void onShowView() {
     super.onShowView();
-
+    commit.onShowView();
     related.setMaxHeight(commit.getElement()
         .getParentElement()
         .getOffsetHeight());