Show stacked icon when a notification's icon goes out of view

Bug: 1002714
Change-Id: Iad2c658e651d5301353ca0db289570d1ea94530a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1865650Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706636}

ash/system/message_center/unified_message_list_view.cc

@@ -287,7 +287,11 @@ std::vector<Notification*> UnifiedMessageListView::GetNotificationsAboveY(
     int y_offset) const {
   std::vector<Notification*> notifications;
   for (views::View* view : children()) {
-    if (view->bounds().bottom() <= y_offset) {
+    int bottom_limit =
+        features::IsUnifiedMessageCenterRefactorEnabled()
+            ? view->bounds().y() + kNotificationIconStackThreshold
+            : view->bounds().bottom();
+    if (bottom_limit <= y_offset) {
       Notification* notification =
           MessageCenter::Get()->FindVisibleNotificationById(
               AsMVC(view)->GetNotificationId());

ash/system/tray/tray_constants.h

@@ -101,6 +101,7 @@ constexpr gfx::Insets kUnifiedSliderPadding(0, 16);
 constexpr int kMessageCenterCollapseThreshold = 175;
 constexpr int kStackedNotificationBarHeight = 32;
 constexpr int kStackedNotificationBarCollapsedHeight = 40;
+constexpr int kNotificationIconStackThreshold = 28;
 constexpr int kUnifiedSliderViewSpacing = 12;
 constexpr int kUnifiedMenuPadding = 8;
 constexpr int kUnifiedMessageCenterBubbleSpacing = 8;