system: Allow keyboard navigation on user drop down menu on tray.

Allows user drop down menu to activatble so that it can be cycled
through.
Add a custom focus search so the drop down menu closes after all items
have been cycled through.
Migrate Closure to OnceClosure.
Make drop down menu a transient child of system bubble.

Test: manual
Bug: 799401
Change-Id: I67af2bb3e58c88f6926ab65ecf565d69325d00b8
Reviewed-on: https://chromium-review.googlesource.com/1038656Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555756}

ash/system/tray/tray_bubble_wrapper.cc

@@ -13,6 +13,7 @@
 #include "ui/aura/window.h"
 #include "ui/views/bubble/tray_bubble_view.h"
 #include "ui/views/widget/widget.h"
+#include "ui/wm/core/transient_window_manager.h"
 #include "ui/wm/core/window_util.h"
 #include "ui/wm/public/activation_client.h"
 
@@ -43,6 +44,12 @@ TrayBubbleWrapper::~TrayBubbleWrapper() {
 
   tray_->tray_event_filter()->RemoveWrapper(this);
   if (bubble_widget_) {
+    auto* transient_manager = ::wm::TransientWindowManager::GetOrCreate(
+        bubble_widget_->GetNativeWindow());
+    if (transient_manager) {
+      for (auto* window : transient_manager->transient_children())
+        transient_manager->RemoveTransientChild(window);
+    }
     bubble_widget_->GetNativeWindow()->GetRootWindow()->RemoveObserver(this);
     bubble_widget_->RemoveObserver(this);
     bubble_widget_->Close();

ash/system/user/user_view.h

@@ -60,13 +60,14 @@ class UserView : public views::View,
   void AddLogoutButton(LoginStatus login);
   void AddUserCard(LoginStatus login);
 
-  // Create the menu option to add another user. If |disabled| is set the user
-  // cannot actively click on the item.
-  void ToggleUserDropdownWidget();
+  // Create the menu option to add another user.
+  void ToggleUserDropdownWidget(bool toggled_by_key_event);
 
   // Removes the add user menu option.
   void HideUserDropdownWidget();
 
+  views::Widget* GetBubbleWidget();
+
   // If |user_card_view_| is clickable, this is a ButtonFromView that wraps it.
   // If |user_card_view_| is not clickable, this will be equal to
   // |user_card_view_|.
@@ -80,6 +81,9 @@ class UserView : public views::View,
 
   views::View* logout_button_ = nullptr;
   std::unique_ptr<views::Widget> user_dropdown_widget_;
+  // Tracks whether |user_dropdown_widget_| was opened with a key event. If
+  // true, HideUserDropdownWidget() will return focus to |user_card_container_|.
+  bool user_dropdown_widget_toggled_by_key_event_ = false;
 
   // False when the add user panel is visible but not activatable.
   bool add_user_enabled_ = true;