Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/wm/aura/wm_root_window_controller_aura.cc

Index: ash/wm/aura/wm_root_window_controller_aura.cc
diff --git a/ash/wm/aura/wm_root_window_controller_aura.cc b/ash/wm/aura/wm_root_window_controller_aura.cc
index 8f099b5d96090775cb3a695a5e58fa3c84430116..9d5d8333cc591df6b998dcd49e27a3bbca5017d8 100644
--- a/ash/wm/aura/wm_root_window_controller_aura.cc
+++ b/ash/wm/aura/wm_root_window_controller_aura.cc
@@ -6,8 +6,11 @@
 
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/root_window_controller.h"
+#include "ash/shelf/shelf.h"
+#include "ash/shelf/shelf_widget.h"
 #include "ash/shell.h"
 #include "ash/wm/aura/wm_globals_aura.h"
+#include "ash/wm/aura/wm_shelf_aura.h"
 #include "ash/wm/aura/wm_window_aura.h"
 #include "ash/wm/common/wm_root_window_controller_observer.h"
 #include "ash/wm/workspace_controller.h"
@@ -76,6 +79,12 @@ WorkspaceWindowState WmRootWindowControllerAura::GetWorkspaceWindowState() {
   return root_window_controller_->workspace_controller()->GetWindowState();
 }
 
+WmShelf* WmRootWindowControllerAura::GetShelf() {
+  return root_window_controller_->shelf()
+             ? root_window_controller_->shelf()->shelf()->wm_shelf()
+             : nullptr;
+}
+
 WmWindow* WmRootWindowControllerAura::GetWindow() {
   return WmWindowAura::Get(root_window_controller_->GetRootWindow());
 }