Adds OnChildWindowVisibilityChanged to ui::WindowObserver

ash/mus/bridge/mus_layout_manager_adapter.cc

Index: ash/mus/bridge/mus_layout_manager_adapter.cc
diff --git a/ash/mus/bridge/mus_layout_manager_adapter.cc b/ash/mus/bridge/mus_layout_manager_adapter.cc
index 58d3ffd097fd142bc40ec4a8101a4739a633bda0..2cada41691fe1e97be1169104cc8bde7f6a06622 100644
--- a/ash/mus/bridge/mus_layout_manager_adapter.cc
+++ b/ash/mus/bridge/mus_layout_manager_adapter.cc
@@ -11,33 +11,15 @@
 namespace ash {
 namespace mus {
 
-MusLayoutManagerAdapter::ChildWindowObserver::ChildWindowObserver(
-    MusLayoutManagerAdapter* adapter)
-    : adapter_(adapter) {}
-
-MusLayoutManagerAdapter::ChildWindowObserver::~ChildWindowObserver() {}
-
-void MusLayoutManagerAdapter::ChildWindowObserver::OnWindowVisibilityChanged(
-    ui::Window* window) {
-  adapter_->layout_manager_->OnChildWindowVisibilityChanged(
-      WmWindowMus::Get(window), window->visible());
-}
-
 MusLayoutManagerAdapter::MusLayoutManagerAdapter(
     ui::Window* window,
     std::unique_ptr<WmLayoutManager> layout_manager)
     : window_(window),
-      child_window_observer_(this),
       layout_manager_(std::move(layout_manager)) {
   window_->AddObserver(this);
-  for (ui::Window* child : window_->children())
-    child->AddObserver(&child_window_observer_);
 }
 
 MusLayoutManagerAdapter::~MusLayoutManagerAdapter() {
-  for (ui::Window* child : window_->children())
-    child->RemoveObserver(&child_window_observer_);
-
   window_->RemoveObserver(this);
 }
 
@@ -49,13 +31,10 @@ void MusLayoutManagerAdapter::OnTreeChanging(const TreeChangeParams& params) {
 }
 
 void MusLayoutManagerAdapter::OnTreeChanged(const TreeChangeParams& params) {
-  if (params.new_parent == window_) {
+  if (params.new_parent == window_)
     layout_manager_->OnWindowAddedToLayout(WmWindowMus::Get(params.target));
-    params.target->AddObserver(&child_window_observer_);
-  } else if (params.old_parent == window_) {
-    params.target->RemoveObserver(&child_window_observer_);
+  else if (params.old_parent == window_)
     layout_manager_->OnWindowRemovedFromLayout(WmWindowMus::Get(params.target));
-  }
 }
 
 void MusLayoutManagerAdapter::OnWindowBoundsChanged(
@@ -65,5 +44,11 @@ void MusLayoutManagerAdapter::OnWindowBoundsChanged(
   layout_manager_->OnWindowResized();
 }
 
+void MusLayoutManagerAdapter::OnChildWindowVisibilityChanged(ui::Window* window,
+                                                             bool visible) {
+  layout_manager_->OnChildWindowVisibilityChanged(WmWindowMus::Get(window),
+                                                  visible);
+}
+
 }  // namespace mus
 }  // namespace ash