Convert //ash from scoped_ptr to std::unique_ptr

ash/shell/window_watcher.h

Index: ash/shell/window_watcher.h
diff --git a/ash/shell/window_watcher.h b/ash/shell/window_watcher.h
index cb28f94e4a197e44c04b01ee30c86888651caf0c..19a1d3434d598d61c3733c0a9a6f4375b4c8544d 100644
--- a/ash/shell/window_watcher.h
+++ b/ash/shell/window_watcher.h
@@ -8,12 +8,12 @@
 #include <stdint.h>
 
 #include <map>
+#include <memory>
 
 #include "ash/shelf/shelf_item_types.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "ui/aura/window_observer.h"
 #include "ui/gfx/display_observer.h"
 
@@ -54,7 +54,7 @@ class WindowWatcher : public aura::WindowObserver,
   // Maps from window to the id we gave it.
   IDToWindow id_to_window_;
 
-  scoped_ptr<WorkspaceWindowWatcher> workspace_window_watcher_;
+  std::unique_ptr<WorkspaceWindowWatcher> workspace_window_watcher_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowWatcher);
 };