Moves maintaining ShellObservers back to Shell

ash/common/shelf/wm_shelf.cc

Index: ash/common/shelf/wm_shelf.cc
diff --git a/ash/common/shelf/wm_shelf.cc b/ash/common/shelf/wm_shelf.cc
index 2a06cc21baa5039b55009c07e6ae45d745dd18c5..ae9d565c3ae16e037376578e45cec228b8dbb07c 100644
--- a/ash/common/shelf/wm_shelf.cc
+++ b/ash/common/shelf/wm_shelf.cc
@@ -168,7 +168,8 @@ void WmShelf::SetAlignment(ShelfAlignment alignment) {
   shelf_widget_->OnShelfAlignmentChanged();
   shelf_layout_manager_->LayoutShelf();
   WmShell::Get()->shelf_controller()->NotifyShelfAlignmentChanged(this);
-  WmShell::Get()->NotifyShelfAlignmentChanged(GetWindow()->GetRootWindow());
+  Shell::GetInstance()->NotifyShelfAlignmentChanged(
+      GetWindow()->GetRootWindow());
 }
 
 bool WmShelf::IsHorizontalAlignment() const {
@@ -212,7 +213,7 @@ void WmShelf::SetAutoHideBehavior(ShelfAutoHideBehavior auto_hide_behavior) {
 
   auto_hide_behavior_ = auto_hide_behavior;
   WmShell::Get()->shelf_controller()->NotifyShelfAutoHideBehaviorChanged(this);
-  WmShell::Get()->NotifyShelfAutoHideBehaviorChanged(
+  Shell::GetInstance()->NotifyShelfAutoHideBehaviorChanged(
       GetWindow()->GetRootWindow());
 }