Re-factor system tray code controlling launcher visibility

ash/system/tray/tray_background_view.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/system/tray/tray_background_view.h"
 
 #include "ash/launcher/background_animator.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/system/status_area_widget.h"
@@ skipping 171 matching lines @@
 
 void TrayBackgroundView::Initialize() {
   GetWidget()->GetNativeView()->layer()->GetAnimator()->AddObserver(
       layer_animation_observer_.get());
   SetBorder();
 }
 
 void TrayBackgroundView::OnMouseEntered(const ui::MouseEvent& event) {
   hover_background_animator_.SetPaintsBackground(true,
       internal::BackgroundAnimator::CHANGE_ANIMATE);
+  UpdateShouldShowLauncher();
 }
 
 void TrayBackgroundView::OnMouseExited(const ui::MouseEvent& event) {
   hover_background_animator_.SetPaintsBackground(false,
       internal::BackgroundAnimator::CHANGE_ANIMATE);
+  UpdateShouldShowLauncher();
 }
 
 void TrayBackgroundView::ChildPreferredSizeChanged(views::View* child) {
   PreferredSizeChanged();
 }
 
 void TrayBackgroundView::OnPaintFocusBorder(gfx::Canvas* canvas) {
   // The tray itself expands to the right and bottom edge of the screen to make
   // sure clicking on the edges brings up the popup. However, the focus border
   // should be only around the container.
@@ skipping 56 matching lines @@
         on_edge ? kPaddingFromBottomOfScreenVerticalAlignment : 0,
         kPaddingFromInnerEdgeOfLauncherVerticalAlignment));
   } else {
     set_border(views::Border::CreateEmptyBorder(
         0, kPaddingFromInnerEdgeOfLauncherVerticalAlignment,
         on_edge ? kPaddingFromBottomOfScreenVerticalAlignment : 0,
         kPaddingFromOuterEdgeOfLauncherVerticalAlignment));
   }
 }
 
+void TrayBackgroundView::UpdateShouldShowLauncher() {
+  status_area_widget()->UpdateShouldShowLauncher();
+}
+
 }  // namespace internal
 }  // namespace ash