Attach panel while dragging to bring it in front of other panels.

ash/wm/panels/panel_layout_manager.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/wm/panels/panel_layout_manager.h"
 
 #include <algorithm>
 #include <map>
 
 #include "ash/launcher/launcher.h"
@@ skipping 220 matching lines @@
     delete iter->callout_widget;
   }
   panel_windows_.clear();
   if (launcher_)
     launcher_->RemoveIconObserver(this);
   launcher_ = NULL;
 }
 
 void PanelLayoutManager::StartDragging(aura::Window* panel) {
   DCHECK(!dragged_panel_);
-  DCHECK(panel->parent() == panel_container_);
   dragged_panel_ = panel;
   Relayout();
 }
 
 void PanelLayoutManager::FinishDragging() {
   dragged_panel_ = NULL;
   Relayout();
 }
 
 void PanelLayoutManager::SetLauncher(ash::Launcher* launcher) {
@@ skipping 307 matching lines @@
   previous_panel = NULL;
   for (std::map<int, aura::Window*>::const_reverse_iterator it =
        window_ordering.rbegin();
        it != window_ordering.rend() && it->second != active_panel; ++it) {
     if (previous_panel)
       panel_container_->StackChildAbove(it->second, previous_panel);
     previous_panel = it->second;
   }
 
   panel_container_->StackChildAtTop(active_panel);
+  if (dragged_panel_ && dragged_panel_->parent() == panel_container_)
+    panel_container_->StackChildAtTop(dragged_panel_);
   last_active_panel_ = active_panel;
 }
 
 void PanelLayoutManager::UpdateCallouts() {
   ShelfAlignment alignment = launcher_->alignment();
   bool horizontal = alignment == SHELF_ALIGNMENT_TOP ||
                     alignment == SHELF_ALIGNMENT_BOTTOM;
 
   for (PanelList::iterator iter = panel_windows_.begin();
        iter != panel_windows_.end(); ++iter) {
@@ skipping 38 matching lines @@
 
     SetChildBoundsDirect(callout_widget->GetNativeWindow(), callout_bounds);
     panel_container_->StackChildAbove(callout_widget->GetNativeWindow(),
                                       panel);
     callout_widget->Show();
   }
 }
 
 }  // namespace internal
 }  // namespace ash