Make toasts notice when they're hidden and send the mouse-out event.

ui/message_center/views/toast_contents_view.cc

Index: ui/message_center/views/toast_contents_view.cc
diff --git a/ui/message_center/views/toast_contents_view.cc b/ui/message_center/views/toast_contents_view.cc
index 93cd95325a76f7fd5265682cd6dfcc2e39a66ce5..02c6e01406c4d9303fc18c34f567c83e6a7831be 100644
--- a/ui/message_center/views/toast_contents_view.cc
+++ b/ui/message_center/views/toast_contents_view.cc
@@ -296,6 +296,12 @@ void ToastContentsView::OnMouseExited(const ui::MouseEvent& event) {
     collection_->OnMouseExited(this);
 }
 
+void ToastContentsView::VisibilityChanged(
+    View* starting_from, bool is_visible) {
+  if (!is_visible && collection_)
+    collection_->OnMouseExited(this);
+}
+
 void ToastContentsView::Layout() {
   if (child_count() > 0) {
     child_at(0)->SetBounds(