ash: Explicitly teach various components about ShelfLayoutManager.

ash/wm/dock/docked_window_layout_manager.cc

Index: ash/wm/dock/docked_window_layout_manager.cc
diff --git a/ash/wm/dock/docked_window_layout_manager.cc b/ash/wm/dock/docked_window_layout_manager.cc
index d79bcaccadb6303f994bcb657ae3b8ad2d708236..d3c73914002c3773a0c788c65a5a6b07b1e95adc 100644
--- a/ash/wm/dock/docked_window_layout_manager.cc
+++ b/ash/wm/dock/docked_window_layout_manager.cc
@@ -426,8 +426,8 @@ DockedWindowLayoutManager::~DockedWindowLayoutManager() {
 
 void DockedWindowLayoutManager::Shutdown() {
   if (shelf_ && shelf_->shelf_widget()) {
-    ShelfLayoutManager* shelf_layout_manager = ShelfLayoutManager::ForShelf(
-        shelf_->shelf_widget()->GetNativeWindow());
+    ShelfLayoutManager* shelf_layout_manager =
+        shelf_->shelf_widget()->shelf_layout_manager();
     shelf_layout_manager->RemoveObserver(this);
     shelf_observer_.reset();
   }
@@ -540,8 +540,8 @@ void DockedWindowLayoutManager::SetShelf(Shelf* shelf) {
   DCHECK(!shelf_);
   shelf_ = shelf;
   if (shelf_->shelf_widget()) {
-    ShelfLayoutManager* shelf_layout_manager = ShelfLayoutManager::ForShelf(
-        shelf_->shelf_widget()->GetNativeWindow());
+    ShelfLayoutManager* shelf_layout_manager =
+        shelf_->shelf_widget()->shelf_layout_manager();
     shelf_layout_manager->AddObserver(this);
     shelf_observer_.reset(new ShelfWindowObserver(this));
   }