Cleanup ash shelf accessor functions.

ash/shelf/shelf.cc

Index: ash/shelf/shelf.cc
diff --git a/ash/shelf/shelf.cc b/ash/shelf/shelf.cc
index 0a02248586537f35ddb025793458a12f53c72db9..c331e66c3359c727e8f5dcfd9014edc715d4bd72 100644
--- a/ash/shelf/shelf.cc
+++ b/ash/shelf/shelf.cc
@@ -18,7 +18,6 @@
 #include "ash/shelf/shelf_navigator.h"
 #include "ash/shelf/shelf_util.h"
 #include "ash/shelf/shelf_view.h"
-#include "ash/shelf/shelf_widget.h"
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/shell_window_ids.h"
@@ -61,14 +60,12 @@ Shelf::~Shelf() {
 
 // static
 Shelf* Shelf::ForPrimaryDisplay() {
-  ShelfWidget* shelf_widget =
-      RootWindowController::ForShelf(Shell::GetPrimaryRootWindow())->shelf();
-  return shelf_widget ? shelf_widget->shelf() : NULL;
+  return Shelf::ForWindow(Shell::GetPrimaryRootWindow());
 }
 
 // static
-Shelf* Shelf::ForWindow(aura::Window* window) {
-  ShelfWidget* shelf_widget = RootWindowController::ForShelf(window)->shelf();
+Shelf* Shelf::ForWindow(const aura::Window* window) {
+  ShelfWidget* shelf_widget = RootWindowController::ForWindow(window)->shelf();
   return shelf_widget ? shelf_widget->shelf() : NULL;
 }