Add not_needed function

tools/gn/function_forward_variables_from.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 
 namespace functions {
 
 namespace {
 
 void ForwardAllValues(const FunctionCallNode* function,
                       Scope* source,
                       Scope* dest,
                       const std::set<std::string>& exclusion_set,
                       Err* err) {
   Scope::MergeOptions options;
   // This function needs to clobber existing for it to be useful. It will be
   // called in a template to forward all values, but there will be some
   // default stuff like configs set up in both scopes, so it would always
   // fail if it didn't clobber.
   options.clobber_existing = true;
   options.skip_private_vars = true;
   options.mark_dest_used = false;
   options.excluded_values = exclusion_set;
   source->NonRecursiveMergeTo(dest, options, function,
                               "source scope", err);
-  source->MarkAllUsed();
+  source->MarkAllUsed(err);
 }
 
 void ForwardValuesFromList(Scope* source,
                            Scope* dest,
                            const std::vector<Value>& list,
                            const std::set<std::string>& exclusion_set,
                            Err* err) {
   for (const Value& cur : list) {
     if (!cur.VerifyTypeIs(Value::STRING, err))
       return;
@@ skipping 192 matching lines @@
     }
   }
 
   // Not the right type of argument.
   *err = Err(what_value, "Not a valid list of variables to copy.",
              "Expecting either the string \"*\" or a list of strings.");
   return Value();
 }
 
 }  // namespace functions