Revert "Fix message_center::MessageView::OnSlideOut UAF"

This reverts commit af5c4bc1.

Reason for revert: Deterministically crashes MSAN and debug CrOS builds, first failure here: https://ci.chromium.org/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/17319

Original change's description:
> Fix message_center::MessageView::OnSlideOut UAF
> 
> Bug: 983009
> Change-Id: Ie285c4035bfc4c45e27e5f3fd6c34280d9f4c2d2
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2001943
> Reviewed-by: Peter Beverloo <peter@chromium.org>
> Commit-Queue: Matthew Denton <mpdenton@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#732131}

TBR=peter@chromium.org,tengs@chromium.org,mpdenton@chromium.org

Change-Id: Ib8a7cfeaa6c81fca58cee2cbff7102a20ca1a474
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 983009
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003167Reviewed-by: Meredith Lane <meredithl@chromium.org>
Commit-Queue: Meredith Lane <meredithl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732224}

ui/message_center/views/message_view.cc

@@ -348,12 +348,11 @@ void MessageView::RemoveSlideObserver(MessageView::SlideObserver* observer) {
 }
 
 void MessageView::OnSlideOut() {
-  for (auto& observer : slide_observers_)
-    observer.OnSlideOut(notification_id_);
-
-  // RemoveNotification() may delete |this|.
   MessageCenter::Get()->RemoveNotification(notification_id_,
                                            true /* by_user */);
+
+  for (auto& observer : slide_observers_)
+    observer.OnSlideOut(notification_id_);
 }
 
 void MessageView::OnWillChangeFocus(views::View* before, views::View* now) {}