GN: Use std::unique_ptr for owning pointers in Scope::NamedScopeMap.

tools/gn/scope.h

Index: tools/gn/scope.h
diff --git a/tools/gn/scope.h b/tools/gn/scope.h
index 72aa0c3e2fb4d04b3124029083e6a337560649f4..e9bd1397cc9b81c76454e44e7c2e6f4eceb3cd78 100644
--- a/tools/gn/scope.h
+++ b/tools/gn/scope.h
@@ -333,10 +333,9 @@ class Scope {
       RecordMap;
   RecordMap values_;
 
-  // Owning pointers. Note that this can't use string pieces since the names
-  // are constructed from Values which might be deallocated before this goes
-  // out of scope.
-  typedef base::hash_map<std::string, Scope*> NamedScopeMap;
+  // Note that this can't use string pieces since the names are constructed from
+  // Values which might be deallocated before this goes out of scope.
+  typedef base::hash_map<std::string, std::unique_ptr<Scope>> NamedScopeMap;
   NamedScopeMap target_defaults_;
 
   // Null indicates not set and that we should fallback to the containing