GN threading refactor

tools/gn/test_with_scope.cc

 // Copyright (c) 2013 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/test_with_scope.h"
 
 TestWithScope::TestWithScope()
     : build_settings_(),
       settings_(&build_settings_, std::string()),
       toolchain_(&settings_, Label(SourceDir("//toolchain/"), "default")),
       scope_(&settings_) {
   build_settings_.SetBuildDir(SourceDir("//out/Debug/"));
 
   settings_.set_toolchain_label(toolchain_.label());
-  settings_.set_is_default(true);
+  settings_.set_default_toolchain_label(toolchain_.label());
 }
 
 TestWithScope::~TestWithScope() {
 }