Revert of Do not activate TrayBubbleView by default

ash/system/tray/system_tray_bubble.cc

Index: ash/system/tray/system_tray_bubble.cc
diff --git a/ash/system/tray/system_tray_bubble.cc b/ash/system/tray/system_tray_bubble.cc
index 76f0a02e87b3f6afea549df598f94522ce3057aa..bf94470ed85f0c75f6784d3d8513fc6c2e1cc0de 100644
--- a/ash/system/tray/system_tray_bubble.cc
+++ b/ash/system/tray/system_tray_bubble.cc
@@ -84,7 +84,7 @@
   DestroyItemViews();
   // Reset the host pointer in bubble_view_ in case its destruction is deferred.
   if (bubble_view_)
-    bubble_view_->ResetDelegate();
+    bubble_view_->reset_delegate();
 }
 
 void SystemTrayBubble::UpdateView(
@@ -210,6 +210,17 @@
   }
 }
 
+void SystemTrayBubble::FocusDefaultIfNeeded() {
+  views::FocusManager* manager = bubble_view_->GetFocusManager();
+  if (!manager || manager->GetFocusedView())
+    return;
+
+  views::View* view =
+      manager->GetNextFocusableView(nullptr, nullptr, false, false);
+  if (view)
+    view->RequestFocus();
+}
+
 void SystemTrayBubble::DestroyItemViews() {
   for (std::vector<ash::SystemTrayItem*>::iterator it = items_.begin();
        it != items_.end(); ++it) {