Allow creation and modification of scopes in GN.

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 {
@@ skipping 165 matching lines @@
   // identifier. It is difficult to write code where this is not the case, and
   // this saves an expensive scope copy. If necessary, this could be expanded
   // to execute the ParseNode and get the value out if it's not an identifer.
   const IdentifierNode* identifier = args_vector[0]->AsIdentifier();
   if (!identifier) {
     *err = Err(args_vector[0].get(), "Expected an identifier for the scope.");
     return Value();
   }
 
   // Extract the source scope.
-  Value* value = scope->GetMutableValue(identifier->value().value(), true);
+  Value* value = scope->GetMutableValue(
+      identifier->value().value(), Scope::SEARCH_NESTED, true);
   if (!value) {
     *err = Err(identifier, "Undefined identifier.");
     return Value();
   }
   if (!value->VerifyTypeIs(Value::SCOPE, err))
     return Value();
   Scope* source = value->scope_value();
 
   // Extract the exclusion list if defined.
   std::set<std::string> exclusion_set;
@@ skipping 33 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