Convert //tools to use std::unique_ptr

tools/gn/builder.h

Index: tools/gn/builder.h
diff --git a/tools/gn/builder.h b/tools/gn/builder.h
index 3a222663438e3b2331c4854dc4f466411d7107e6..04459760246605e6534dc523a5ed4427b7de4158 100644
--- a/tools/gn/builder.h
+++ b/tools/gn/builder.h
@@ -33,7 +33,7 @@ class Builder : public base::RefCountedThreadSafe<Builder> {
 
   Loader* loader() const { return loader_; }
 
-  void ItemDefined(scoped_ptr<Item> item);
+  void ItemDefined(std::unique_ptr<Item> item);
 
   // Returns NULL if there is not a thing with the corresponding label.
   const Item* GetItem(const Label& label) const;