Remove top and bottom margins from TrayBubbleView

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index 9ba78008b750a4c7c8f56c4ef144f8f7ad3f9d0e..1fff3878f6a7c68fab99e8ec6fbcdbb2483ade90 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -402,10 +402,8 @@ void SystemTray::ShowItems(const std::vector<SystemTrayItem*>& items,
       // This is the case where a volume control or brightness control bubble
       // is created.
       init_params.max_height = default_bubble_height_;
-      init_params.top_color = kBackgroundColor;
       init_params.arrow_color = kBackgroundColor;
     } else {
-      init_params.top_color = kBackgroundColor;
       init_params.arrow_color = kHeaderBackgroundColorDark;
     }
     init_params.arrow_offset = arrow_offset;
@@ -470,7 +468,6 @@ void SystemTray::UpdateNotificationBubble() {
   TrayBubbleView::InitParams init_params(anchor_type,
                                          GetAnchorAlignment(),
                                          kTrayPopupWidth);
-  init_params.top_color = kBackgroundColor;
   init_params.arrow_color = kBackgroundColor;
   init_params.arrow_offset = GetTrayXOffset(notification_items_[0]);
   notification_bubble_.reset(