Fix infinite recursion on hiding panel when created during fullscreen mode.

ash/wm/panels/panel_layout_manager.cc

Index: ash/wm/panels/panel_layout_manager.cc
diff --git a/ash/wm/panels/panel_layout_manager.cc b/ash/wm/panels/panel_layout_manager.cc
index 2592337c24c195e671a4b3822b140be5036bbef6..95db2579663de31a3b66a63e6778f8b6b7496015 100644
--- a/ash/wm/panels/panel_layout_manager.cc
+++ b/ash/wm/panels/panel_layout_manager.cc
@@ -371,7 +371,6 @@ void PanelLayoutManager::OnWindowAddedToLayout(aura::Window* child) {
     panel_info.slide_in = true;
   }
   panel_windows_.push_back(panel_info);
-  child->AddObserver(this);
   wm::GetWindowState(child)->AddObserver(this);
   Relayout();
 }
@@ -388,7 +387,6 @@ void PanelLayoutManager::OnWindowRemovedFromLayout(aura::Window* child) {
     delete found->callout_widget;
     panel_windows_.erase(found);
   }
-  child->RemoveObserver(this);
   wm::GetWindowState(child)->RemoveObserver(this);
 
   if (dragged_panel_ == child)
@@ -402,6 +400,8 @@ void PanelLayoutManager::OnWindowRemovedFromLayout(aura::Window* child) {
 
 void PanelLayoutManager::OnChildWindowVisibilityChanged(aura::Window* child,
                                                         bool visible) {
+  if (visible)
+    wm::GetWindowState(child)->Restore();
   Relayout();
 }
 
@@ -481,12 +481,6 @@ void PanelLayoutManager::OnPostWindowStateTypeChange(
     RestorePanel(window_state->window());
 }
 
-void PanelLayoutManager::OnWindowVisibilityChanged(
-    aura::Window* window, bool visible) {
-  if (visible)
-    wm::GetWindowState(window)->Restore();
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // PanelLayoutManager, aura::client::ActivationChangeObserver implementation: