Ash Tray: Fix message center visibility when collapsing with no notifications.

This CL also adds unit tests for the collapse/expand behaviour for the message
center.

TEST=manual + new unit tests
BUG=1019405

Change-Id: I1189549e41e6f11f2d513c4d041de6e5ac108caf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888187
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711131}

ash/system/message_center/stacked_notification_bar.cc

@@ -362,4 +362,4 @@ void StackedNotificationBar::ButtonPressed(views::Button* sender,
   }
 }
 
-}  // namespace ash
\ No newline at end of file
+}  // namespace ash

ash/system/message_center/unified_message_center_bubble_unittest.cc

@@ -259,6 +259,7 @@ TEST_F(UnifiedMessageCenterBubbleTest, ReverseFocusCycle) {
 
 TEST_F(UnifiedMessageCenterBubbleTest, CollapseState) {
   EnableMessageCenterRefactor();
+  AddNotification();
 
   GetPrimaryUnifiedSystemTray()->ShowBubble(true);
   int small_display_height =

ash/system/message_center/unified_message_center_view.cc

@@ -122,7 +122,7 @@ void UnifiedMessageCenterView::SetAvailableHeight(int available_height) {
 }
 
 void UnifiedMessageCenterView::SetExpanded() {
-  if (!collapsed_)
+  if (!GetVisible() || !collapsed_)
     return;
 
   collapsed_ = false;
@@ -132,7 +132,7 @@ void UnifiedMessageCenterView::SetExpanded() {
 }
 
 void UnifiedMessageCenterView::SetCollapsed(bool animate) {
-  if (collapsed_)
+  if (!GetVisible() || collapsed_)
     return;
 
   collapsed_ = true;