Convert //ash from scoped_ptr to std::unique_ptr

ash/host/ash_window_tree_host.h

Index: ash/host/ash_window_tree_host.h
diff --git a/ash/host/ash_window_tree_host.h b/ash/host/ash_window_tree_host.h
index f9ac376f9bc268b9f54fa5545c3196fe6b2a4c6f..bf9afa49ae38a989df35b988f30f8f6b1725da80 100644
--- a/ash/host/ash_window_tree_host.h
+++ b/ash/host/ash_window_tree_host.h
@@ -5,9 +5,10 @@
 #ifndef ASH_HOST_ASH_WINDOW_TREE_HOST_H_
 #define ASH_HOST_ASH_WINDOW_TREE_HOST_H_
 
+#include <memory>
+
 #include "ash/ash_export.h"
 #include "base/callback_forward.h"
-#include "base/memory/scoped_ptr.h"
 
 namespace aura {
 class Window;
@@ -62,7 +63,7 @@ class ASH_EXPORT AshWindowTreeHost {
   virtual void UnConfineCursor() = 0;
 
   virtual void SetRootWindowTransformer(
-      scoped_ptr<RootWindowTransformer> transformer) = 0;
+      std::unique_ptr<RootWindowTransformer> transformer) = 0;
 
   virtual gfx::Insets GetHostInsets() const = 0;