Convert //ash from scoped_ptr to std::unique_ptr

ash/frame/caption_buttons/frame_size_button.h

Index: ash/frame/caption_buttons/frame_size_button.h
diff --git a/ash/frame/caption_buttons/frame_size_button.h b/ash/frame/caption_buttons/frame_size_button.h
index 84cf84839c22a39cb0562253fb5d5bccddcf58eb..839f98e0df4de28606984df28568be2b530f3378 100644
--- a/ash/frame/caption_buttons/frame_size_button.h
+++ b/ash/frame/caption_buttons/frame_size_button.h
@@ -112,7 +112,7 @@ class ASH_EXPORT FrameSizeButton : public FrameCaptionButton {
   // Displays a preview of how the window's bounds will change as a result of
   // snapping the window left or right. The preview is only visible if the snap
   // left or snap right button is pressed.
-  scoped_ptr<PhantomWindowController> phantom_window_controller_;
+  std::unique_ptr<PhantomWindowController> phantom_window_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameSizeButton);
 };