Make a layer for popup MessageView

ui/message_center/views/message_view.cc

Index: ui/message_center/views/message_view.cc
diff --git a/ui/message_center/views/message_view.cc b/ui/message_center/views/message_view.cc
index abc66f3b8fc55ff3168ee48ef34f28686aa2f450..79ad8b09ea8f821b49f55b9c140f695669d7c672 100644
--- a/ui/message_center/views/message_view.cc
+++ b/ui/message_center/views/message_view.cc
@@ -67,6 +67,8 @@ MessageView::MessageView(MessageCenterController* controller,
       notification_id_(notification.id()),
       notifier_id_(notification.notifier_id()),
       slide_out_controller_(this, this) {
+  SetPaintToLayer();

[Eliot Courtney, 2017/05/19 04:32:49]

Maybe add a comment as to why this has to be here?

+  layer()->SetFillsBoundsOpaquely(false);
   SetFocusBehavior(FocusBehavior::ALWAYS);
 
   // Create the opaque background that's above the view's shadow.
@@ -99,8 +101,6 @@ gfx::Insets MessageView::GetShadowInsets() {
 
 void MessageView::SetIsNested() {
   is_nested_ = true;
-  SetPaintToLayer();
-  layer()->SetFillsBoundsOpaquely(false);
 
   const auto& shadow =
       gfx::ShadowDetails::Get(kShadowElevation, kShadowCornerRadius);