ui/aura: Use base::string16 now that string16 was moved into base namespace.

ui/aura/window.h

Index: ui/aura/window.h
diff --git a/ui/aura/window.h b/ui/aura/window.h
index e2c0d83bb97f748853635c24c18e93292c24a2fa..baf34f15663cffc72dbaef1a560e6c75c3810232 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -93,8 +93,8 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   const std::string& name() const { return name_; }
   void SetName(const std::string& name);
 
-  const string16 title() const { return title_; }
-  void set_title(const string16& title) { title_ = title; }
+  const base::string16 title() const { return title_; }
+  void set_title(const base::string16& title) { title_ = title; }
 
   bool transparent() const { return transparent_; }
   void SetTransparent(bool transparent);
@@ -486,7 +486,7 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   int id_;
   std::string name_;
 
-  string16 title_;
+  base::string16 title_;
 
   // Whether layer is initialized as non-opaque.
   bool transparent_;