Convert //ash from scoped_ptr to std::unique_ptr

ash/wm/workspace_controller.cc

Index: ash/wm/workspace_controller.cc
diff --git a/ash/wm/workspace_controller.cc b/ash/wm/workspace_controller.cc
index bea54a92fc346d5a5d8bc9612dad011b8f0bf7cc..a47772720ef2668bcca22e63888865589f40e00a 100644
--- a/ash/wm/workspace_controller.cc
+++ b/ash/wm/workspace_controller.cc
@@ -134,7 +134,7 @@ void WorkspaceController::DoInitialAnimation() {
 }
 
 void WorkspaceController::SetMaximizeBackdropDelegate(
-    scoped_ptr<WorkspaceLayoutManagerDelegate> delegate) {
+    std::unique_ptr<WorkspaceLayoutManagerDelegate> delegate) {
   layout_manager_->SetMaximizeBackdropDelegate(std::move(delegate));
 }